>how is it possible without the typical "root access / rootkits" invasiveness of anticheat software!?

It probably does require root/kernel access. If you're not a fan of that, your only option is cloud gaming.

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.

You can use HyperV to get around that, if youre inclined to do so.

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.