Though I would recommend doing it like this to test it out. Change sddm to lightdm (or whatever greeter you have running now) if needed.
systemctl stop sddm.service
systemctl start ly.service
If that all works out, then you can make it permanent by:
systemctl disable sddm.service
systemctl enable ly.service
Otherwise, reboot if you’re locked up or something and you’re still in sddm.