Actually, when I uploaded stuff on YouTube I’d notice sometimes that it was best to, even if the source footage was 1080p, upscale / upload it at 4k or 8k resolution so that people with sufficiently good internet could view it without as much compression. (In fact, when the original video uploaded is upscaled to 4k, even the 1080p version of the final video looks closer to the source footage)
These were unlisted videos, so I’m not a YouTuber or anything, but I’m pretty sure this is one thing some people do to make their videos appear better sometimes