Not counting the Steam Deck, since KDE isn’t actually turned on while you’re running games.
Normally I’m a Gnome guy, but I’m building a tiny low power portable computer and wanting to keep resource utilization low, so I’m investigating other options.
I just stick to Gnome to avoid problems in gaming specifically, but obviously Plasma works great as well on Steam Deck.
You could give LXQT a shot, which should be QT-compatible, and maybe require less fussing with if you do run into an issue. Xfce or Mate might be options as well, but not as lightweight.