I should mention one other caveat: if you uninstall Juliaup, it won’t uninstall the Julia versions that you installed using juliaup, i.e. all of those Julia versions will stay around in ~/.julia/juliaup! In a way this is now similar to the situation with packages and artifacts that you install using Julia: those are also not removed when you uninstall Julia from your system.
I’m not super happy about that aspect of things, but a) it is not clear to me right now how I could fix this easily and b) it seems in line with packages and artifacts, so I think at the moment the general rule just is that to really get rid of Julia on your system you need to uninstall it and delete your .julia folder.