Had the same issue, but only when my usb mouse was plugged in. I’ve seen others where having a monitor connected produces the same problem.
https://universal-blue.discourse.group/t/sddm-not-starting-if-usb-mouse-connected/11217
https://github.com/ublue-os/bazzite/issues/3376#issuecomment-3591905221
The solution for me was to:
create /etc/systemd/system/sddm.service.d/udev-settle-wait.conf
[Unit]
Wants=systemd-udev-settle.service
After=systemd-udev-settle.service
and reboot