I have the same problem. I believe it is a bug in iOS 15 beta 4 and macOS 12 beta 4. It happens only when a 3rd party app is built against the new iOS 15 / macOS 12 SDK. Full error message: <CKError 0x60000197dcb0: "Account Temporarily Unavailable" (36/1028); "Account temporarily unavailable due to bad or missing auth token">  Submitted a feedback: FB9411756

Same problem. Submitted a bug report (FB8889904)