With the Qt 5.15.7 update that landed in Rawhide recently - https://bodhi.fedoraproject.org/updates/FEDORA-2022-5a466cce73 - sddm seems to consistently crash, leaving the system at a black screen on boot. Unfortunately I can't get a usable backtrace yet, gdb is just giving me question marks everywhere. This should be easy to reproduce with e.g. https://kojipkgs.fedoraproject.org/compose/rawhide/Fedora-Rawhide-20221102.n.0/compose/Spins/x86_64/iso/Fedora-KDE-Live-x86_64-Rawhide-20221102.n.0.iso . This is an automatic F38 Beta blocker per "Complete failure of any release-blocking image to boot at all under any circumstance - "DOA" image (conditional failure is not an automatic blocker)" - https://fedoraproject.org/wiki/QA:SOP_blocker_bug_process#Automatic_blockers .
Looks like this was due to a missing rebuild of layer-shell-qt, which uses private Qt symbols and so needs rebuilding even if the API doesn't change. I've done that rebuild now, marking as ON_QA so we can confirm with the next Rawhide compose.
yes, it did fix this.