Forgejo, a Gitea fork used by Codeberg. I chose it because it’s got the right balance of features to weight for my small use case, it has FOSS spirit, and it’s got a lovely package maintainer for FreeBSD that makes deployment and maintenance easy peasy (thanks Stefan <3).
The feature request includes the phrase “Behind the scenes there would need to be some cryptographic magic,” because it’s just yet another “I have a sweet idea for an app, bro, I just need you to do the coding for me” pitch.
The project has 766 contributors with pull requests being accepted all the time. That’s not a walled garden.