[int_19h]

I think the point is that this needs to be made clearer in the official docs from the get go.

[woodruffw]

It's said explicitly in the second sentence in the usage docs[1].

> Attestations are currently only supported when uploading with Trusted Publishing, and currently only with GitHub-based Trusted Publishers. Support for other Trusted Publishers is planned. See #17001 for additional information.

[1]: https://docs.pypi.org/attestations/producing-attestations/