I'm having a similar issue. I am using an older "broken" laptop with Intel graphics. I had HDMI video output on whichever version of 10 I was previously using (10.95.1, maybe?). I updated to 11, and lost video out of the HDMI port. Audio is passing thru the port no problem. I get video to the TV during boot at the LibreElec splash screen (and when powering down), but as soon as the Kodi splash screen comes up, it cuts out. Kodi is not showing me any options to routing video thru HDMI.
I added "video=LVDS-1:d" to the APPEND string in /flash/syslinux.cfg, but nothing changes after I save it and reboot
LibreELEC:~ # tail /sys/class/drm/*/status
==> /sys/class/drm/card0-DP-1/status <==
disconnected
==> /sys/class/drm/card0-HDMI-A-1/status <==
connected
==> /sys/class/drm/card0-LVDS-1/status <==
connected
==> /sys/class/drm/card0-VGA-1/status <==
disconnected
Thank you for any wisdom you may have to share!