Those numbers in the hundreds of thousands (often referred to as "liquidated" in the numbers published by the Ukrainians) contain killed, missing, Pow and injured. Also those numbers are likely inflated for obvious reasons: this is an information war just as much as one on the battlefield. There are some sources (Oryx on Twitter for example) and people who digest those kind of sources (Perun on YouTube for example) I suggest watching to be as good informed as possible. And yet there will still be copius amounts of disinformation, propaganda and fake news on both sides and we probably have to wait years afters this war has ended to know at least some truths.

I think I read a few weeks ago it was like 200k-300k for Ukraine and closer to 400k-ish for Russia, but Russian numbers are hard to verify.

This is extremely difficult to count, even years later.

Think of a bomb that failed to detonate during the war, and 20 years later some kid finds it and it explodes in their face. Think of people who got injured during the war in a way that shortened their lives and they died a decade later. Think of the generation of traumatized soldiers who will have a higher probability of developing an alcohol addiction which can lead to death. It's really difficult to know how many people died because of a war even years after it ended.

Ukraine wont claim their death toll is high, but, every country at war, want to lie and pretend that is not the case, for morals.