Do any Git servers support patch sets (i.e., contrib without forks)?

A puzzle: patch sets have been with Git since the beginning; why do none of the Git hosting platforms seem to support that workflow?

Is there a service or self-hosted option for exposing my repository in a way that allows contributions without requiring contributors to first create their own fork (and thus also host their fork publicly).

The simplest version of what I want would be a "Merge/Pull Request" workflow initiated by uploading a patch/diff instead of creating a fork and requesting a merge from that fork.

One of the goals is accessibility: ideally anyone could click "Edit" on a file in the web UI to start a "Patch Request."

I've searched extensively for this and haven't come up with much. GitLab and GitHub require contributions to come from forks or branches of the original repo. (Frustratingly, both of them also exclude the option to merge with unrelated histories and have no option for subtree merges.) Bitbucket, Gitea, Gitbucket, etc. appear to use the same process, but I couldn't definitively confirm that. Linux & co use a process of managing patch sets through mailing lists, and I don't understand how they operate, let alone be able to replicate a simpler version of that myself.

I've come across other folks asking for similar features, so I know I'm not alone, but my searches of HN didn't turn up much here, so I'm hopeful there are some fresh ideas here.