I tried the command you provided in a Plasma 6 Wayland session, and the GUI that opens for YaST as a result is still blurry and not Wayland-y:
su - root -c sh -c "WAYLAND_DISPLAY=$XDG_RUNTIME_DIR/$WAYLAND_DISPLAY /usr/sbin/yast2"
Also xeyes
is able to track my cursor when it passes over that window and it is the one in focus, so it’s an X11 window