I run games in a VM to isolate things. Some anti-cheat detect a VM and just assume you’re a cheater and exit the game, but I just don’t play those games.
Sometimes, yes. However last time I tried to get Hyper-V nested in KVM to work it…didn’t. Windows’ nested virtualization on AMD is a bit unsupported and buggy.
It probably does require root/kernel access. If you're not a fan of that, your only option is cloud gaming.