Please only use the LibreELEC Hyperion addon and the LibreELEC Hypercon version to configure it (see this Wiki page for details Hypercon [LibreELEC.wiki]).
I might have a worse problem.. Playing videos of 720p and up incl youtube gets me "no signal" on my RPi 4 using hyperion, the lights change color correctly :(. Tried with hypercon from the hyperion-project, removed it, and I have also tried using the libreelec addon. Tried powering through GPIO and using a beefier adapter (Oneplus 15W Dash charge adapters), no luck. Everything was fine and dandy with RPi 3
Removing the 4k option in config and limiting it to 1080 incl GUI doesn't work.