I’m running into the same issue now. My build was rejected because of GameKit.
First of all the Unity guide on how to prepare your app for macOS App Store submission is about 60% current-- I had to search for workarounds to fix the rest. It took me several days just to get a .pkg that could upload at all via Application Loader and then wasn’t immediately rejected by Apple right after at the Application Loader stage but before the AppStore Connect submission.
Secondly, this GameKit / GameCenter bug is OLD-- I’m seeing posts from [as far back as 2014]( [URGENT]MAC App review team rejected because GameKit framework linked! page-4) about it.
Why doesn’t Unity understand we should be able to just push a button, get a packaged binary we can upload with Application Loader to the macOS App Store. That should be a checkbox on the Build Settings. Or, yes, at the very least, create an Xcode project like iOS and tvOS and go from there. This current delivery process where we literally have to use terminal to hack our apps is insane.