+1 me too. This is really frustrating. Filing "feedback" with Apple, hopefully it bears fruit.

I've got the same problem - "ITMS-90338: Non-public API usage - The app contains or inherits from non-public classes in My_App_Name: NSConstantArray". But I tried building with Xcode 12 and the problem persists - I haven't included any new 3rd party frameworks since the last submission, but it's a huge project with quite a lot of them. At this stage I've also no idea how to track down exactly where this NSConstantArray is being found. Incredibly frustrating. Will watch this space...