As I recall gitlab has an edit function. Not sure if it's the best alternative today, but it's one I worked with and know it can edit and can be self hosted. ( I went back to using git over ssh to a bare debian server and have no regrets )

Edit: I briefly thought about forgejo (a gitea clone) after seeing it in self hosted, but I have no need for it ( just yet.)

Gitlab has an online web editor and can be self hosted.

(Though it’s a bit of a resource hog)

Forgejo (Gitea fork used by codeberg.org) is a lightweight self-hostable option, and has a web-ui-based file editor. It's got an official docker image, and it's packaged for freebsd, as well, which makes it very easy to deploy and maintain either containerized or on a server.