I run a bog standard bookworm + kde. Only needed to update kernel from backports when I replaced my aging 1060 with an rx6750xt for more recent amdgpu firmware. Games run just fine. Solid as a rock.
Awesome stuff! I'm running KDE as well - can't wait for Plasma 6 to start hitting the repos to get HDR on CP2077.
I have an even newer GPU so a more current kernel was needed. I went with testing because I prefer to follow a more up-to-date system, and it's almost as solid as stable so I don't see many downsides. I wouldn't do it on a server but on the desktop I can easily work around or fix whatever minor nags appear.
I really wanted to get Mesa from experimental though as it follows upstream pretty closely (just a few days lag usually), and testing being generally closer to it probably helps. Or not, I haven't really tested that assumption. :D