Can you check the installed version of the qt6-qtwayland package, by running dnf list --installed qt6-qtwayland ?
If it’s 6.9.1-2, then you could try downgrading to 6.9.1-1 as per 2375356 – qt6-qtwayland 6.9.1-2 breaks KDE Plasma lockscreen, requiring user to drop to TTY to unlock session
6.9.1-2 seems to particularly break the lockscreen, but some users have reported it causing broader problems.
UPDATE: a fixed version of qt6-qtwayland,6.9.1-3, has now been released into stable Fedora 42. So a normal sudo dnf upgrade --refresh should fix.