I keep finding piecemeal examples of things that can go into a .github directory on a GitHub repository.
I can see that it is used for GitHub actions and workflow and for Pull request and issue templates, but I can't see a page outlining what you can put in there with ideally some documentation. I also think I've seen a funding example too.
Basically every time I see something you can do there, I think "that's neat I should do that", but other than examples I can't see a way to discover new things other than by example.
Due to the fact that the directory is called .github it seems to defy Google and SO search as well.