Same for me.
Bought a new Raspberry Pi 4 and installed the latest version of Libreelec (10.0.2).
It worked fine on my office screen, but when I connected it to an old TV, the screen is black and the TV shows that there is no contact.
TV is completely black when starting up to TV.
I have tested a lot of tips and made changes to both config.txt and cmdline.txt but nothing seems to work.
So I need help moving forward.
All tips are gratefully received.