Had the same problem on fedora (no issue on bazzite, nobara, or arch). First time it was xwayland that kept crashing without a display present for some reason, second time I never solved since I was distro hopping the fedora family of distros but it seemed to be a problem with SDDM
It still starts the KDE session, but it's probably on another term output. Hit ALT+F1 and see if it shows, but it depends on the distro, so it could F1, F6, F7...etc
F1 is just a blank conosle with a blinking curses and you can't type anything into it. F2/3/4 open a new terminal from where I can log in, but none seem to have a KDE session running. Gotta check out the other F keys. Just in case none of the work, is there a solution you know of?
You're probably on a laptop and have multiple GPUs enabled at the same time. If not, you're defining Nvidia drivers with something trying to be smart about when to enable the actual outputs or not.
You can either make sure to have the display turned on, or make it super clear to the drivers to always enable a display regardless of whether it detects a display.
Boot log/kernel/dmesg, X/Wayland/kde primarily. Been a long time since I've had to troubleshoot something like this so I don't know the new kids on the block. Maybe upstart or dracut? Whatever manages the boot process now