Mac (and Linux) isn't supported by Unity as a library so it can't be supported.
Windows was a work in progress but never got completed (see the next bulletpoint).
But I believe Flutter platform views on windows aren't fully functional yet, so maybe it isn't feasible yet.
The repo owner isn't really active anymore, he shows up maybe 1-2 times a year. He publishes pub.dev updates so those are rare.
I try to do some maintenance to keep my own app working, and those fixes usually end up on the master branch. But don't expect new features.
support for this widget is listed as: Android, iPad OS, iOS, Web
Is there a reason why Macos would not be supported? (and windows)
Also, is there current state of this repo far ahead of what is currently on pub dev?
Edit: the pub dev that comes up first on google is apparently not the latest