I upgraded the RPi4 from 12.0.2 to 12.2.1 and had HDMI problems.
After first reboot the TV screen looked shifted. I the system settings only 1024x768, 800x600 and other typcal PC monitor resolutions were offered. The HDready resolution was not listed. HDMI audio did also not work and was not listed as an option.
(my setup is an old Panasonic plasma TV with HDready resolution connected directly to the RPi4. The sound is played by the TV over the HDMI interface)
Starting with the second reboot the TV did not show the KODI logo. Only, the "12.2.1" message is displayed - then the TV picture stayed dark.
I flashed another µSD card with the old version 12.0.2 and booted this image. The "12.0.2" message was shown, but still the boot process seemed to stop (no KODI logo displayed and the TV stayed dark). - and this was the LibreELEC version that was used for months (of course with working TV and sound)!
The solution for me.
In the end I connected a 24" fullHD Samung PC monitor to the RPi4 with the 12.2.1 µSD card. (The old monitor just has VGA and DVI inputs - so, an DVI to HDMI adapter was used). The RPi4 successfully booted LibreELEC.
Then the HDready TV was reconnected - and picture and HDMI sound work as expected.
The kids use it for several days without a problem.
I hope, this is of help for some LibreELEC users.
Thank you for making LibreELEC.
Michael