Same on the older few. I'm not sure I understand it though, seems strange you can have a tag for a commit that's only present in a fork?

Is it perhaps a bit misleading, and only means that there's no branch containing that commit?

Git doesn't have a concept of "fork".

GitHub uses this metaphor, and, as another commenter already aptly described, it could be nothing more than a fancy name for namespaced branches, on the server side.

On the client side, "forks" are usually different repository clones with different remotes and a "coincidentally" shared history.

But you can also map forked repos to multiple remotes of the same repository for example, instead of folders.

Assuming that forks would live in separate clones/blobs on the server is not really based on anything, so I think the warning is a good middle ground between explaining what forks are and how they handle them, and giving actionable advice.

It's also better suited for PR:

"Fork me on GitHub"

vs

"Branch and push your own clone on GitHub, using our shared blob optimizations".

I think the warning is clear and there's nothing misleading about it, but others have already pointed this out and git can be tricky.

Similar issue with "Merge request", GitHub invented the term "Pull Request" (aka PR, lol).

But they combined that term it with a particular workflow (rebased, ff-only merged without merge commits favored), and it worked well for them, and also to simplify Git for their users.

So it was positive sum PR at the time, when they started, I was still taught Subversion and CVS at uni, and at the time, many people consired them simpler, and pondered SVN as the most reasonable middle ground to the decentralized concept of Git!

There is little difference between a tag and a branch in git. There is just the convention that tags reference the same commit forever, while branches move.

On github forks are part of the same physical repository. You could imagine that each logical repository is just a namespace for branches and tags, backed by the same physical repository.

I do consider the warning a bug if github, it should check both tags and branches for commits which are to be considered part of a logical repository.

It can mean either, it's a consequence of how github optimized their backend storage so a 100 forks of a repo initially take up the same space as 0 forks

main (or master) is just another branch to git.