hi,
are you sure you using the HDMI Port closest to the usb-c power?
Tried that port, but it won't even throw a signal to the TV. Port 1 works perfect until a stream is selected. It plays audio, and the controller is visible, but the video signal stays black. I have not edited the config files yet, but at this point, my rpi3 works fine, so I probably won't do it. I've reassigned my 4 to some IoT tasks and I'll wait for the bugs to be fixed before trying libreelec on it again.