Yeah, I wanted to try it on my (GitLab) repo as well, but it also said "No repositories found". Clicking "Index any public repo" pops up a dialog that says "Search for a GitHub repository" and "or Enter the URL of a public GitHub repository".
So looks like it's not actually any repository.
Yeah, the site is pretty ambiguous. It says “any repository”, but they require a GitHub URL.
That explains why none of the projects which I tried worked.
I wonder why they’d use a descentralised protocol but then only support a single host.