We are getting the exact same error it is a nightmare! Are we really being forced by Apple to update to Xcode 12 or they won't accept our apps to Testflight etc ? In our case we are using Xcode 11 and had no issues up until yesterday. Now our attempts to submit to Testflight are being met with this error.

Totally agree with the poster, its like Apple are being monopolistic and forcing devs to update.