Gitea works on a feature for federated pull requests, so you can make pull requests over different instances, but the next thing i found on my gitea instance is the ability tonapply a patch on the website itself as an logged in user.
(Tried on https://gitea.com/gitea/tea/src/branch/main/README.md)
Edit: IIUC, Gitea doesn't support this yet. https://github.com/go-gitea/gitea/issues/13508
(Side note: it's odd to me that Gitea hosts its source code on GitHub.)