(PlaMo developer here)
Screen rotation largely depends on DRM driver (vc4 in case of raspberry PI I assume?) and also very recent kernel. I did some lookup and it seems to me that weston does support it so should work in theory with kwin_wayland as well ™️
But since this is not case, Can you please send me logs of kwin_wayland, (See wikipage on how to setup debugging) and dmesg?
You can reach out to be on Freenode (bshah), or email firstname.lastname@example.org