I've searched Apple's documentation, open source projects, and Google, and I cannot seem to find any information about SwiftPM.SPMRepositoryError error 5. Heck, I can't even find information about SwiftPM.SPMRepositoryError.
Does anyone know of documentation for this error or the error codes?
What worked for me was switching to ED25519 key.
I think this is happening now because of the effort to improve Git protocol security on GitHub. You can read more about it here: https://github.blog/2021-09-01-improving-git-protocol-security-github/
There you can see the timeline. The final step was put into motion two days ago: