Problem
Multiple users have reported that Fedora 43 KDE sometimes boots to a black screen.
Cause
This seems to be a problem with handoff from ‘plymouth’ (the component that displays a graphical boot process) to ‘sddm’ (the login manager used on KDE). The fact that it only affects some users/systems suggests that there’s a race or timing issue involved. Most people seem to be running AMD iGPUs, but we have some reports with other GPUs as well.
Related Issues
Bugzilla report: #2404966
Workarounds
Several users have reported that disabling the graphical boot process avoids the problem. This will give you a somewhat uglier text boot process. It doesn’t have any other consequence.
You can do this permanently by running sudo grubby --update-kernel=ALL --remove-args=rhgb. To reverse this once the bug is fixed, you can do sudo grubby --update-kernel=ALL --args=rhgb.
If you want to test the change temporarily first, or you can’t manage to boot far enough to run that command, you can edit the arguments at boot time from the Fedora boot menu. If the Fedora boot menu does not appear on your screen, try pressing Esc or F8 repeatedly while the system is booting. On the Fedora boot menu, hit e to edit the default boot entry, go down to the line that starts linux, press End to go to the very end of the line (or use arrow keys). It will likely end rhgb quiet. You want to go back through the word quiet and delete the word rhgb. Then hit Ctrl-x to proceed with boot.