Hi Sam,
Just to remind ourselves the very first post here describes the problem well. Many of us with this issue have disabled CEC or run an old image. I’m running OSMC_TGT_vero3_20220314.img.gz
I can provide you SSH access if it will help and can change firmware.
The workaround mentioned that didn’t work for me (others have said it worked for them) can be found HDR Autoswitch causing issues on my LG OLED65C8 - #239 by kaspik
Please to hear you don’t think Vero5 has the issue.