I have an offline PC at home, and I wanted to test Linux editor there, but found that the only way to get it was using Unity Hub. Why?
I noticed it too but managed to reverse engineer a link from other links and parts that I found. This short Reddit post by me may be of interest:
https://www.reddit.com/r/Unity3D/comments/dau7p9/lets_talk_linux/f1upkr1/
It is pretty annoying. There is a thread with direct download links somewhere but it was only updated to 2019.1 and probably does not include every version.