The manpower situation favors Russia in every way. First of all, 80% of the casualties come from artillery fire and Russia fires around ten times more artillery than Ukraine. This means that Ukraine is taking far more casualties than Russia in this war. This is reflected in Ukraine now having expanded its conscription to older men and even women. This wouldn't be needed if Ukraine wasn't running out of manpower. On the other hand, Russia isn't doing conscription or mobilization right now, and they raised around 300k volunteers over the past year.

Russian casualties corroborated by publicly available data as of 20 October stand at 34,857. We can also see how the casualties are steadily dropping since March

On the other hand, even western media admits that Ukrainian casualties stand at over 100k now. Again, given that Russia has a much bigger population, it's pretty clear that this is a catastrophic situation for Ukraine. It's also important to keep in mind that the trained and motivated troops Ukraine loses cannot be easily replaced. You can't just throw somebody into training for a few weeks and expect them to be an effective fighting force that's going to take on a seasoned and experienced army.