It seems you are doing an external test.
If this is the case, then "Waiting for Review" means you haven't submit your build to the App Store Connect. For external test, your build should be reviewed and approved.
Once your app is approved, the test begins. It can last for 90 days. But you may stop the test when you wish to.
AEIOU
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I also had this problem and haven't got ideas on this.
I used an embarrassing way: I made a SKScene (SpriteKit scene) on the view and changed the scene's background color :D
Yes, UI API can only be called on the main thread.
This error occurred at the very beginning when you initialize the label.
So before you code ran up here, had you executed your code in background?