Some classes aren't meant to be subclassed (based on their documentation).
Example: RPScreenRecorder , there's a sharedInstance property that returns the only valid instance.
Making classes sealed also:
* Makes us able to generate less code for the bound methods (they don't have to be virtual, and can assume nobody will override them, so their implementation can be simpler)
* Makes the registrar able to just skip those types completely, no processing needed.
Unfortunately the generator completely ignores the [Sealed] attribute on types, it's only honored on methods.
Merged in master https://github.com/xamarin/xamarin-macios/commit/44f14cf768f0ab82b185eb03cd4053a7da403b96