Can you explain what "breaks" you are experiencing?
I'm running Fedora/KDE/Wayland on two machines here, and the only oddity I get regularly is on my system with one monitor in landscape and one in portrait. Sometimes half of the landscape screen seems to be funky until I turn the portrait monitor off and on again (almost like it is trying to put the two displays on one for some reason). Most everything else has been flawless.
The panel freezes after a short time using it. I can't play a lot of my games because the mouse doesn't work when it opens. The monitor position always changes but that happens on x11 as well.
Running Wayland/kde on endeavourOS here. It has gotten so much better in the last couple of updates. I used to have stutters and just random plasmashell carshes. Those are gone now. Only major annoyance I still have now is some apps are still blurry, which is not Wayland's fault of course, and sddm when I wake the machine from suspend always turns into a black screen with a warning that the session is locked and I need to unlock it with ctrl-alt-F and run loginctl-unlock-session 9 (or some random number). Id do that and it unlocks. It's so weird, and not a big deal, but kind of annoying.
Yes and no. X11 is the old window system for Linux (and most Unixes), but it was very much not designed with security in mind, and has become difficult to maintain to the point that the only new updates made to it are to help with Wayland backwards-compatibility. Wayland is its de facto successor, and most new Linux desktop development is based on Wayland rather than X11.
It really depends if you are using GNOME or KDE ( or something else ).
GNOME in Fedora defaults to Wayland already I believe. In Plasma 6, due to first ship in Fedora 40, support for Wayland will be complete. That is why they are targeting the switch for then.
Plasma 6 is KDE using the Qt6 GUI toolkit so the KDE in Fedora 40 will be quite different from the KDE in Fedora 38 today. Today, KDE is built with the Qt5 toolkit and only partially supports Wayland.
GNOME is built with a GUI toolkit called GTK. The current version is GTK4 and that will still be the version used in Fedora 40. GTK has supported Wayland since GTK3.