Mycorrhiza has multiple source-code repositories. This hypha lists them and explains what are their roles.
The main repo is GitHub. It is the most popular repository of the three, most people reach out for Mycorrhiza here. The development is actually held there. GitHub releases are made. Sadly, it is somewhat ideologically wrong, so we don't fully trust it. The code is mirrored from here to other places.
SourceHut is ideologically closer to us, we even write git tag messages especially so they show up on SourceHut. It's not handy to use though.
Codeberg is a newer addition to the collection. It is like a middle ground between the two others. Codeberg releases are not made.
Each Mycorrhiza repo is accompanied by a Mycomarkup repo.
There used to be a Gitea instance hosted by u/Bouncepaw that hosted a mirror too, but it's down. Even if it's still online, don't use it.