I doubt its a libqt5pas issue, more likely a Wayland related one.
I have noted in the past that KDE always seems a bit less Lazarus-QT5 friendly, and I find that very strange !
Newest release of Gnome on Ubuntu, Fedora and Debian all seem to be a bit more QT5/Wayland friendly, sad if Arch is heading the a different direction. I don't test my app against Arch, takes too effort to keep a VM up to date. But sounds like I need to test more against KDE/Plasma. Sigh.
Davo