Thanks for the contribution!

As the regex only applies to REST paths, I would move the regex replacement code into an if (appState.repoLocation.prefix == "rest") branch, also to document what it's trying to match.

The regex also won't match rest paths of the form https://user:pass@host:8000 (note the missing trailing /), but I'm not actually sure if restic allows them. But it won't match sftp path then either?

You're right, i didn't think about ports, will have to check. But you're right i'm missing quite a few test cases. Thin i was focusing on here wasmainly that we can have the protocol optional in the URL (diallowing the URL() from js).
Let's collect all cases interesting to blur out here, and then adjust.

I actually tried to design it to work with any URL, rest but also sftp, ftps or any future URL like path. Ports and the whole path after the domain are now more leniently handled. Care to have a look?

Looks good to me. Thanks!