I think global immigration would be much reduced, the regimes in Europe aren't going to allow immigration from the colonies like IOTL. Algeria and Angola were settler colonies historically and so it's likely that they would continue to be settled by Europeans and so would have much higher European populations, especially since IOTL the Europeans fled during decolonization. Libya and Tunisia will also be heavily settled by Italians to the point that Italians might even become a majority in Libya. I wonder if we might see some settling of Slavs as a kind of foreign legion, fight in Africa to get some land and avoid being killed by the Germans. I'm not sure if that's realistic or not but the Germans will have a lot of Slavs and it might be tempting for the smaller countries to use them that way if they can't get enough of their own people to move to or fight in Africa.
Immigration to the US will be changed too, I expect the Vietnamese, Laotian, and Cambodian communities will be virtually non existent as the wars in Southeast Asia will be butterflied away. There might be increased Russian immigration from whatever is left of the Soviet union.
Finally I'm not sure where Britain's place is going to be in all this. But they are very quickly be put in a hugely awkward position. In a Nazi victory timeline colonialism will quickly become a dirty word among the US population, which brings us back to to Britain. Which now finds herself in an anti colonial block while owning the worlds largest empire... super awkward. Decolonization will have to happen quickly but I'm not sure what form it will take. Just simply giving independence exposes weak African states to aggressive fascist regimes. But keeping parts of the Empire into the 60s as IOTL is quickly going to prove untenable. We might see a defense union or a more powerful commonwealth, or even something like the EU. I imagine England might have loser immigration policies to show that they are different from the other European powers. I also expect British Africa to stay more or less democratic as that is probably a condition of British protection.
And thanks for the compliment

I find this a really interesting timeline.