It's on the radar (as Gitea is also actively working on this - https://github.com/go-gitea/gitea/pull/35295), but I suspect you can not expect anything for a while:

"Upstream Proposal: Repository Grouping/Subgroups in Forgejo":

https://codeberg.org/fedora/forgejo-deployment/issues/224

"feat: extend Forgejo URL structure from organisation/repository to organisation/project/repository":

https://codeberg.org/forgejo/forgejo/issues/9550