Xwayland doesn’t get input in some special way, it uses the exact same Wayland protocols to get input events as native Wayland apps. All claims about it being more complete or anything like that are nonsense.
Krita forces Xwayland because they have some X11 specific code they haven’t bothered porting away from, that’s all.
That’s a terrible example, because they completely ignore the many many years old standardized APIs (screen casting and remote desktop portals) that they could use, in favor of doing hacky and broken things that require root access instead.