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.
No DE. Currently on DWL, but I’ve used Hyprland, River, Sway, Qtile, SperctWM, BSPWM, XMonad and Awesome (from most recently configured, to the first one I ever used) . I have used both GNOME and KDE at times where I didn’t have anything else on the system yet, I’ve used Cinnamon full time in the beginning, and I use a lot of XFCE apps as a part of my setup, notable examples being Thunar and Ristretto (and I used to use xfce4-screenshooter).