However, I wondered about how much activity there still is on this. Isn't this considered mostly finished at some point?
I can understand that there might be some more development on libfuse but that is independent anyway. As far as I remember, the MacOS state of libfuse was somewhat unclear?
A really good example of File Provider API is the Secure ShellFish app on iOS / iPadOS - https://secureshellfish.app .
I consider it buggy and unusable. At least on Mac. Definitely not finished.
I gave up on it and switched to using VSCode's remote development extension.
Not ideal if you're a Linux distribution trying to figure out which fork to pick up, but ideal if you're an upstream maintainer trying to find someone responsible.