> apply high quality compression on videos that become popular

Do they put a different amount of compression effort in if the video isn't (expected to become) popular?

I don't know what the Youtube compression queue looks like.

I'd not be shocked if they do more aggressive compression for well known creators.

For nobodies (like myself) the compression is very basic. Whatever I send ends up compressed with VP9 which, I believe, youtube has a bunch of hardware that can do that really fast.