Try my YouTube channel at
https://www.youtube.com/@Mixerrog/videos to see if it shows a 5.1 setting please? If it does & plays in some kind of surround, it is a simulated surround which I suspect done by your browser device?
I have tried to upload 5.1 wav files & YouTube always converts them to stereo 128k AAC files. I have read that all files on YouTube are strictly stereo also.
I just used JDownloader2 to download the Peter Gabriel video above & it's audio is a opus format which it's
Codec info in VLC shows as stereo only & the mp4 file shows stereo only also. I then converted the opus file to flac which resulted in stereo only file so I am pretty sure any surround from YouTube would be a fake version done by the browser device converting the stereo file to a surround.
Rog