In theory yes. In practice most X11 applications can be ran using Xwayland as a compatibility layer
Additionally any application using a GUI toolkit (like kde, qt or gtk etc) only needs to to update to a version that has native Wayland support. Which means most applications already support it. At least if they don't use any X11 APIs directly (which is not that common).
Not really a GUI toolkit but many many games use SDL and they also gain wayland support with a library update
In theory yes. In practice most X11 applications can be ran using Xwayland as a compatibility layer
Additionally any application using a GUI toolkit (like kde, qt or gtk etc) only needs to to update to a version that has native Wayland support. Which means most applications already support it. At least if they don't use any X11 APIs directly (which is not that common).
Not really a GUI toolkit but many many games use SDL and they also gain wayland support with a library update