What if Nazi Germany did not invade Poland?

[ReluctantSamurai]

See the Soviet Offensive in Manchuria.

The Soviet offensive against the Japanese Kwantung Army was done almost entirely with existing units moved east from the European theater of operations.

of course operation Bagration.

Bagration and the other major Soviet offensives of 1944 and 1945 were made possible, in part, by LL which allowed the Soviets to conscript from the worker population that otherwise would have had to be on the farms or in the factories.

At they still didn't include 13 years old boys and 63 years men.

Stalin could reasonably expect to arm and mobilize any citizen capable of drawing a breath and pointing a rifle.

I could quote some sobering statistics from Mark Harrison's book Accounting for War: Soviet production, employment, and the defense burden 1940-1945, but this probably isn't the place for it. Suffice it to say, the Soviets were scraping the bottom of the barrel for manpower (one good indication is the reduced size of rifle divisions from earlier in the war; another is that even by 1950, Soviet population and production had not yet returned to pre-war levels). They had been consistently conscripting from the farm and factory workers pool. When LL comes to an abrupt end (as it would in a ww3 scenario with the Western Allies), then in order to keep some semblance of production numbers to make up for LL, population is going to have to be shifted back to the farms and factories, not the other way around.