YouTube tends to post a downscaled SD version first, then they encode and post the higher-res versions when they get around to it. This can take days in some cases. Meanwhile the creator catches the flak...
You don't need high res for HDR on YouTube (144p HDR is a thing there oddly enough) and the 4k version had already processed when I posted that comment (with no change since in HDR availability). Usually media announcements/large channels pre-upload the video so it's ready when they want it to actually publish to avoid that kind of issue though.
4K processing takes just minutes, but HDR processing can take over a month to… never. There is no indication of this at all, no progress bar or eta. Just check manually every few days!
This is why everyone is giving up on HDR, it’s just too painful because the content distributors are all so bad at it, with Netflix being the sole exception.