For many victims we'd not even know - for example about 50000 civilians have been killed by Russian forces in Mariupol and many bodies are inside the ruined buildings which Russia is just demolishing right now without taking the bodies out.
A lot of people on occupied territories - government/municipal officials, former military, journalists, activists, etc. - have already been kidnapped by the Russian SS force ("Russian Guard") and nobody knows and may never know the fate of the many of them.
About million of people have been moved into Russia - they are moved through "filtration camps" where those who deemed "nationalist" (anti-Russian posts in FB/Twitter for example or having family members who have fought on Ukrainian side) are filtered out and again fate unknown. The fate of the rest is officially some resettlement in Russia though there is no way to account for all of them.
Also a note about the Putin regime actions to erase the memory of the millions of victims of another mass killing - during recent years Russia de-facto outlawed (assigned impossible to exist with status of "foreign agent" which led to the organization closing) to the "Memorial" organization the main work of which was maintaining the public memory of the victims of the Stalin repressions.