If public key is denied forgejo is setup, but you have an old connection in your authorized_keys file probably form using gitea. Remove the line, it should prompt you to accept public key on next ssh session. This is a basic ssh functionality probably why you were downvoted I guess.

Gitea and forgejo configs were 100% same at some point, check forgejo news for when the last version that supported gitea migrations. That said it should still be pretty close.

Velero is the backup solution for PVCs and k8s way.