Fedora is pretty stable itself, but I have experienced some problems with KDE, for instance dolphin crashing on opening a directory attached by KDE Connect. Keyboard shortcuts seem to work just fine, but they may be not configured the way you expect, so consider tweaking them in the settings, no difficulties here.

Also, keep in mind KDE is quite a heavy environment, it may feel slow after Xfce, even on a middle-end system. Personally, I would probably choose GNOME if I returned to the past moment of installing Fedora.

Fedora is based on Red Hat, you'll need time to get used to some minor differencies in contrast to Ubuntu, especially commands' syntax. You'll have to reinstall all needed programs, relogin your accounts and so on. I think you will generally be able to copy and paste some configs, but they may need a bit of adjustment.

While it is quite stable, Fedora still recieves updates really frequently, you should ask yourself if you really want to update every week or two.

If you use Xfce with X11, be ready to face Wayland's specifics with screen recording and working with monitors.

My conclusion: KDE is probably not an optimal choice, but switching to Fedora is worth it, if you are ready to spend a day or two getting known with it's specifics.