It's more I don't have them all checked out, and a good chunk are mirrors of github, so I'll have to list out each one and push to a new remote, mirrors will have to be setup again, and I also use the container and package registries. I'm pretty embedded. It's not impossible, but it's a weekend project for sure.
If you are using containers, it should be fairly trivial. Otherwise, there might be some renaming to do, but Forgejo should be 100% compatible with Gitea (at least right now). Just make sure you have a good backup in case anything would happen.