Meanwhile I'm wondering whether you're running with fbdev X driver for some reason. Maybe intel modeset kernel driver is broken or disabled for some reason. Can you provide the Xserver logfile somehow? Unfortunately I don't know where to find it when using sddm as displaymanager. Maybe it's still /var/log/Xorg.0.log or it's in ~/.local/share/xorg or somewhere else or hidden somewhere in journalctl. :-(