Right, this isn't an
early Weimar/preempting Weimar revolution then; it waits until quite some time after The Great War and the Entente allies are terribly distracted themselves.
So, we've PODed (or whatever the right verb is--it's not "butterflied," these aren't chaotic random events but the stipulated divergences) away both the Bolsheviks and the Nazis. Now I'm trying to visualize how European politics would have gone under those circumstances.
No USSR/Third International to kick around and rally support behind right-wing authoritarians in a desperate struggle to contain Russian socialism. No, instead we have a right-wing White Russia to gratify any Red-baiter's heart.
But
first the February then October Revolutions had gone forward presumably much as OTL. Thus, although obviously there was some early divergence that led to the ultimate defeat and collapse of Bolshevism, perhaps the Leninists had first signed Brest-Litovsk, then Imperial Germany did collapse as per OTL, leaving the borders and regimes of Eastern Europe up in the air and not settled until after the Whites took over in Russia. At this point in the narrative Kairos still has a lot of wiggle room to retcon plausible backgrounds to a wide range of possibilities to the east of Germany. We don't know yet for instance what the status of the Baltic nations is, or Finland (which I guess we can just term a fourth Baltic if we want to, or lump into Scandinavia...or it could be a conquered Russian province again, along with some or all of the others). We don't know where Poland stands, with what sort of borders and what sort of leadership. I presume Pilsudski is in the mix somewhere. If Poland is independent, what sort of relations does it have with Russia? Not so great presumably, but maybe a lot better than OTL with the USSR.
The thing is, the Western Entente members presumably do recognize and support the Russian regime as a successor to their Tsarist wartime ally. Of course that regime did collapse, the Bolsheviks presumably published the prewar (and during-war) secret treaties to embarrass all the bourgeois powers collectively, so the new Russian regime is not technically owed anything under those treaties. Thus, since presumably Poland and Finland and the other Baltic nations probably did spin off into independence, and I for one doubt that the new victorious Whites were a lot more militarily capable than OTL Red Army under Trotsky, if any of the eastern European nations are back under Russian rule, it would have to be because Western allies at some point or other supported that takeover, to tip the balance.
I doubt they'd do that, and I think they would try to restrain the Russians from any adventures on their own hook. For one thing, presumably Americans did join the Allies, Wilsonian polemics about freedom and self-determination and all that went much as OTL, Russia was down for the count during the critical years right after the war, and I guess the League of Nations exists to try and stabilize things. From the point of view of competing great powers, it is probably better to have lots of little regimes more or less dependent on Western diplomatic support, military aid, and so on to prop them up versus the reviving Russian colossus, then to try to keep the Bear happy by feeding it.
OTOH, OTL Eastern Europe was very largely a beneficiary (if that is the right word!

) of Western interest in holding a
cordon sanitaire as they called it against the Soviet Union; the Western Entente presumably has far less interest in messing around there ITTL, and some interest in trying for friendly relations with Russia.
Part of the whole Eastern European mess OTL was that the Wilsonian principle of nationalism conflicted with the principle of democracy. Demographically, there was no way to simply draw lines around neat clusters of distinct nationalities; the borders as they did emerge OTL never were satisfactory in terms of where people actually lived. Every recognized nation in the East had substantial numbers of their nominal nationality living in some other nation, and lots of people who were either of one of their neighbors' peoples or third nationalities that had no state at all.
We are I suppose all familiar with Stalin's massive demographic intervention after OTL WWII regarding Poland and Germany. The Soviets grabbed huge tracts of former eastern Poland, grabbed somewhat smaller tracts of eastern Germany to compensate the Poles--but this was only half the project--they also forced massive migrations, of Germans out of the newly Polish territories, Poles out of what remained of Germany into the new Poland, and Poles out of the former eastern Polish territories now part of the USSR. The thing is, this sort of thing was done pretty much everywhere in the future Warsaw Pact zone. It was only possible to speak of coherently national countries whose borders contained the large majority of their nominal people and not much of others after a lot of people got moved.
Presumably without post-WWII conditions, this sort of reshuffling and upheaval in people's lives was impossible. Nor would anyone countenance the survival of the great empires that had allowed the sort of mixed situation that was reality on the ground to exist; Austria-Hungary was surely doomed long before this timeline's various PODs start to become decisive; Germany surely would have been at least as dismantled as OTL if not more so; Russia was out of the picture until long after the dust largely settled. Ragtag, motley Ruritainian nations it is then, and so presumably most or all of them (except Czechoslovakia) would have been under some sort of quasi-aristocratic, military dictatorships, perhaps blessed with some nominal (or effectively autocratic) monarchy to paper things over with some semblance of coherence not based on naked coercion.
I think it is important to at least settle where Germany's borders with Poland were. Would it be largely as OTL?
OTL, after Stalin reorganized things (and of course huge numbers of people, including the vast majority of Poland's Jews, who had been a very large minority before WWII, were horribly dead) Poland was/is IIRC about 90 percent Polish--but in the interwar period OTL, it was more like 70 percent or less. Not only the Jews but a lot of Belarussians were under the Polish flag, as were a substantial number of Germans and I don't know who else. If ITTL Poland was even more successful in the East then their hegemony would be that much more diluted (and Russia would have an even bigger irredentist issue--though I presume that the right-wing mad dogs we have running Russia here wouldn't be satisfied with anything less than pre-Great War boundaries and more--they'd be as much the enemies of any kind of Poland as Hitler was OTL I'd think, though probably more open to some shadowy nominal Polish existence as a puppet kingdom or duchy). But if they get even more to the west, from Germany, they'd have even more Germans than OTL and again the same sorts of problems to the west with Germany.
I'm thinking that in the 1920s the British and French, working in the League and behind the scenes diplomatically, tried to stabilize things between Poland and Russia, but if forced to a choice would favor Poland if Poland were anything close to a stable regime. Now, with a Red Germany, they will seek to shore up Poland even more and also to broker some sort of Holy Alliance with Russia as well.
---
What about Western and German domestic politics?
The failure of the Soviet Union to survive means that working-class politics is deprived of a standard to rally behind--but also, is relieved of a highly polarizing controversy. This matters internally to the Left, which probably holds together under some sort of more or less reconstituted Second International, though ITTL the Bolsheviks did have some years to rally the radicals to a Third International and now, with the loss of their center, these radicals might not be welcome back nor comfortable in those ranks again. After all many who joined the Third International were the minority of radical Socialists who refused to accept the nationalism of the majority of their comrades.
And yet here we have the OTL leaders of German Communism leading the whole Social Democratic ensemble, or at any rate a decisively large fraction of it. Presumably then the Independent Social Democrats in Germany did more or less make their peace with and work their way back into the SDP--or alternatively, the latter disintegrated completely (or mostly) and leftists attracted a lot of former Socialists into their more radical organization. Not having Stalin around to twist the various parties of the International to putting his Russia/Stalin interests first makes that seem plausible to me.
I am not sure if there is any reason to think that things went a lot differently in Britain or France than OTL. Their domestic socialists would not be polarized by the controversy between the Internationals, but neither would the bourgeois parties be either panicked or cowed by the threat of a new and more radical international movement. Until Kairos or the evolving logic of the timeline determines otherwise, I'm going to presume it was largely a wash and the two big western Entente powers went through pretty much the same domestic politics as OTL. Presumably the Entente's big shots disapproved of German socialism of any stripe (well, some of them were Labour or allied with the British left and I suppose in principle would say they'd smile on "reasonable" German socialists--but define that, naively or cynically, in an unrealistic way that guarantees they hate actual German socialists). But given how things went OTL, where the SDs were the closest thing to a solid basis of support the Weimar Republic had, and they were more scrupulous than other parties about accepting Versailles in principle (and using their stance of reasonable compliance to negotiate better terms, notably from the Americans who stood outside the Versailles system) I guess the Anglo-French would have gotten pretty complacent about the German left and might have been far more worried about the German right--especially with a right-wing Russia for them to ally with and no Soviet boogeyman to fear.
Thus I suppose it is not implausible that a radical, Communist movement might have been evolving among German socialists, ready to seize the moment of the Depression, and yet not be noticed seriously by Britain and France until too late.
I leave it up to you, Kairos, to describe how exactly that happened!
I am interested in going forward with this. Meanwhile, we have a newly Communist post-Weimar Germany, of not yet described exact boundaries. I imagine that culturally and economically things went there much as OTL in the 1920s, meaning that we have the whole legacy of Weimar-era art, and Dr Hugo Eckener is a respected figure worldwide (especially in the USA) who has been happily flying the Graf Zeppelin all over the world. Well, perhaps it was not possible ITTL to operate over Russia as he did OTL quite a few times, including the famous world-circling flight--perhaps he managed to get along well enough with the Russians to do some of that, or took a much more southerly route across Eurasia--which would have been a longer flight but would have demonstrated the proposed British Empire route--Med to Cairo to India, extending to Singapore before hooking north to Japan and thus as OTL across the Pacific to the USA.
I don't mean to hijack this for Zeppelin-wank, but I do think it is interesting to specify how Eckener and the Luftschifftsbau Zeppelin interacts with the Revolution. OTL, German leftists tended to disapprove the company's cozy relationships with the government and Dr Eckener was a liberal in the European sense--definitely not a socialist, though definitely benign in his notion of a properly ordered society that ought to be decent to ordinary people in some fashion.
I can see him going either way--either fleeing to the West (presumably to the USA and Akron, Ohio, to try to consolidate his operations with Goodyear's), or getting coopted into more or less supporting the new German regime, and perhaps helping stabilize relations with both domestic German moderates and foreign countries, notably the USA.
If FDR gets elected as OTL I can definitely see a sort of diffuse quasi-alliance arising between American New Dealers and the new Germany, if it survives a couple years and doesn't alienate too many American moderates too much.
But just how panicked will the British and French be in the meantime--bearing in mind that if the bourgeois classes are scared out of their wits, meanwhile a lot of working people will be cautiously or enthusiastically optimistic. If the upshot of the Entente powers is that they take a hard line, that will mean that democracy is probably suspended in those nations...