Intercepts isTypeSupported() calls by YouTube and lies about HDR support being available.
If this has no effect on yours, please edit the code of the script by removing the // on this line:
//console.log('testing for: '+ type);
Then, when you load a video, the script will dump out a list of all the different codecs YouTube is checking for to the Web Console.
I think the interesting ones will contain
eotf so you can filter the Web Console on that as a first approximation.