If rustup is the normal way to install rust, then that is exactly what I'd want to use. My employer would mirror the needed web sites. For example, my employer mirrors much of github and ubuntu and various Microsoft things. I just follow the normal instructions to fetch things on the internet, and it all works from the mirrored web sites.

It’s the default choice, yes. However, If you’re using Ubuntu you could also install it through apt, though you’ll get an older version.

Note how Ubuntu does things correctly, using signatures on the packages. I can copy those to any web site.

Doing things that way helps you too. Mirrors, including caches, are easy to set up.

Installing via apt will not work for Windows users.

Sure, we check signatures too. (At least, Cargo does. I think rustup may not in some circumstances? I forget) It's about defense in depth.

I am a Windows user, I know that. That's why i said "if" :)