package.json in /Asset/Rivet in the Github, the version now reads {{VERSION}} seemingly in order to make your buildchain easier. So I then tried to download the v2.0.0rc-1 release from Github and install that. I added the Rivet folder to my Assets folder and it seemed happier with that, did a recompile, and kicked up a bunch of C# warnings for warning CS8632: The annotation for nullable reference types should only be used in code within a '#nullable' annotations context. but those are fine. I then tried to open the Rivet window in Unity, and then I get a few more warnings: