Interesting, I have an rx 6800xt, and have also updated the system, this happens shortly afterwards Shutdown sometime stalls, monitor turns off, pc stays on - #9 by Henrrypoop . But somehow changing back to sddm, lets me shutdown, instead of a stall. Might try to downgrade this, and go back to plasmalogin.
EDIT: JUST SHUTDOWN WITH SDDM, still the same, this happens so sporadically, I don’t even know, gonna try to downgrade the firmware via downgrade package.