Edit: looks like, of course, they can ban you and lose access to your games, however it requires threatening legal action against Valve.
https://www.oneangrygamer.net/2020/06/steam-user-loses-game-...
Looks like this user received this message[0] after being banned from the community and only because he mentioned russian law did Steam suspend his account.
> Going to support and blalblab again my rights and the russian law, they slapped me with a perma community ban and 1 month ban to contact the support.