Escape Login Loop in Fedora

The problem seems to be caused by an update to SDDM (Simple Desktop Display Manager).

On Fedora it can be downgraded, but first you need an internet connection. I enabled my wireless internet connection by running:

nmcli connection up <wireless-network>

Where <wireless-network> is the SSID of my wireless network.

I then downgraded SDDM:

sudo dnf downgrade sddm

Logins should then work after a reboot.