If xwayland is disabled (which is the default and recommendation for secureblue), the KDE Plasma splash screen takes extremely long to disappear and actually enter into the desktop. (~30 seconds on my end)

This is upstream, but I understand the KDE developers response as basically WONTFIX, due to them not disabling xwayland upstream.

Disabling the KDE splash screen fixes this issue and immediately loads into the desktop like expected.

I don't see an important reason for needing a splash screen, while the UX improvement of removing it for the sake of a significantly faster startup time is outweighing in my opinion, at least until this may get fixed upstream at some point.

My argument for having this as a default feature is that many users likely may not realize that this is actually a bug and attribute the long startup time to something else, just give secureblue the "fault" for this or just don't know how to research the reason for this in the first place.
(It isn't obvious that this is caused by xwayland, I only noticed this out of pure coincidence)