I actually disagree with Tsouras that with the WAllies out of the war Stalin would go all out. When Stalin went all out OTL it was when he had German forces divided onto two fronts.
"Roosevelt has given his word that extensive action will be mounted in France in 1944. I believe that he will keep his word. But even if he does not, our own forces are sufficient to complete the rout of Nazi Germany."
Stalin said that to Zhukov in December 1943, right after returning from the Teheran Conference. Given how far the Red Army had come and how far the Wehrmacht had fallen by then, he was probably right.
I honestly see given the Soviets OTL were running really low on manpower
Not quite. Soviet losses in 1944 were quite comfortably below their replacement capacity. When Operation Bagration began, for example, the Soviets had a half-million replacements who had finished training and were waiting assignment to formations. And they ultimately suffered only 2/3rds that in irrecoverable losses.
Compare this to the Germans, who had dropped the age of conscription to 16, were now contemplating forming militia units with children as young as 12, and were still finding themselves constantly lacking any pool of men to draw upon, and it is exceedingly clear that the Red Army isn't really facing that much of a manpower crisis. Their not in the position of 1941-1942 where they could lose several million men in a month and increase the size of their army, but they are perfectly capable of replacing the vastly lower loss rates of 1943-1945.
Given the timing, this amounts to an annoyance for the Soviets at most. Their domestic industry and agriculture have been recovering since the start of '43. By mid-1944, they are well beyond the point where lend-lease is necessary for their victory.
and if they haven't decisively broken the German lines by the time Trinity
They definitely will have. By 1944-45, the Red Army as a military force was not just superior to the Wehrmacht quantitatively but qualitatively as well.