OEM install does not work since at last Plasma 6 but maybe before I've updated the oem-prepare/prepare-user/calamares-oem-prepare2 script to use kwriteconfig6 and remove use of plasmapkg which set the theme, however it'll still need a theme set somehow However it doesn't start SDDM on reboot unless you change the oem-config.target to want multi-user.target instead of basic.target. I don't know what's wrong with basic.target. If in doubt blame Wayland?
fixed in all editions