Russia continued WW1 with a civil war that lasted until 1922. Their military deaths were quite evenly split between the world war stage and the civil war stage.
A) Lots of Russians died during WW2, it wasn’t “evil Russia sends troops from occupied republics to fight for them while Russians sit back”.
B) Lots of mercenaries from post-Soviet republics fight for money on Russias side now
C) Russia didn’t pull out because they’ve run out of men. Where did you get this?
There are a couple of good WWI documentaries on YouTube which you can watch for free. You'll find that C) is the truth.
I wonder where then the millions of soldiers that fought the russian civil war came from.