This is Unity's fork of the .NET Runtime repository.
The difference between this fork and the upstream repository should be as small as possible, with all of the differences specific to Unity. Our goal is to upstream as many changes made here as possible.
There is a job in Unity's internal CI which runs weekly to pull the latest code from the upstream dotnet/runtime repository main branch and create a pull request to merge these changes to the unity-main branch.
When a pull request is open against this fork, we should determine if the changes in that pull request should be pushed upstream (most should). Ideally, pull request should be organized so that all changes in a given pull request can be directly applied upstream. Any changes specific to the Unity fork should be done in a separate pull request.
Assuming the branch with changes to upstream is named great-new-feature then a new branch of upstream main named upstream-great-new-feature should be created. Each commit from great-new-feature should be cherry-picked upstream-great-new-feature, and then a pull request should be opened from upstream-great-new-feature to main in the upstream repository.
It is acceptable to merge changes to this fork from great-new-feature before upstream-great-new-feature is merged, but we should at least open an upstream pull request first.