@nichtich There are many more related tickets, see the collection by @pere at https://codeberg.org/ForgeFed/ForgeFed/issues/174 .
Also, @hugopeixoto recently tried to get NLnet funding for such a project (but it was rejected): https://forum.forgefriends.org/t/federation-in-gitlab-nlnet-grant-proposal-maybe-december-2022/933 .

@a has been working on adding #ForgeFed support to #forgejo / #gitea for some time now: https://codeberg.org/forgejo/forgejo/issues/59

Though currently there seem to be no plans to add federation to GitLab, I am optimistic that we will see federated forges emerging in the not-too-far future.