> Was a long term XFCE user (this was long before lxde became popular) because Gnome/KDE felt too heavy for my old computers.

Apparently, recent KDE versions are actually one of the lightest resource DEs available, which has been great.

IME[0], that's only true for the X11 session, which is snappy, while the Wayland flavor feels sluggish and uses more CPU. Some distros are switching to Wayland by default so might be worth trying both and see what runs best on your machine.

[0]: Possibly hardware-related? Older Intel mobile 4c here.