Did you ever get your app working in Xcode and able to publish it? I've run into the same problems with Xcode upgrades from 11 to 12. Apple Dev is useless so far. It's a serious problem. Was there any resolution for you?

Hi, I wonder if you were ever able to figure this out? Since installing Xcode 12.2 I've had Error ITMS-90283 when I've tried to publish 2 different apps. Both had been published twice in the preceding 5 months with Xcode 11.x These are both Mac apps. I'm dead in the water until I can get beyond this. Maybe just wait for Xcode 12.3 to come out.