>
Isn’t that another war crime. >

Kinda.
Renouncing Ukrainian citizenship isn't the main issue. The main issue is gaining Russian citizenship. The moment they become Russian, they can be mobilized and sent fight against their own. The moment they become Russian, they're not allowed to leave the region as those regions are under martial law.
In other words, by forcing people to become Russian, they're making them legal mobiks which becomes a war crime as it's against international law to use people from invaded territory as your invasion force. They'll be used as cannon fodder.
And if they don't, they'll get deported which is in itself a form of genocide or they'll get jailed which can also become a type of genocide as they'll probably be jailed/reeducation camp. >

They should all resign en masse. See how Russians can "govern" without anyone local to do it. >

They don't care about governing. They'll just abduct, relocate, imprison, rape, torture and kill anyone that doesn't do what they're told. Which I guess if I think about it, that's just Russian 'government'.