Looking at the Xcode 12.5.1 release notes, I see no reason why you would need to update your app. If Xcode 12.5 is working for you, keep using it to develop your app.

@testable import is for importing Swift modules, such as your app, not individual classes. Replace the class name with the name of your app (or framework) target, and you should be able to access your app's classes in the unit tests.

I cannot reproduce your issue. I do not get the error message on Xcode 12.5 on macOS 11.4 when I create a new iOS game project that uses SpriteKit and run the project on an iOS simulator. The project runs and the spinning nodes appear when tapping/clicking in the simulator.