I’m using EndeavourOS with KDE.
The display is correctly oriented when logged in but it doesn’t rotate correctly when I’m logged out.
EDIT: corrected the post. This happens when logged out, locking the screen has it displayed correctly.
I never configured anything on X with a DE, let it be KDE, Gnome or Cosmic, but configure everything with config files I can just copy on sway. It has nothing to do with X or Wayland, but the DE/WM you use.