Xcode rejects the build as it is "not accepting apps developed with this OS yet". Based on the experiences of prior summer beta cycles — when should one expect this blocker to come down. Will I be waiting all the way until the public release of Sequoia (or longer)?
When do we expect apps built with Xcode 16 and macOS sequoia 15.1 to be able to upload to TestFlight?
When Apple tell you that you can submit apps built with Xcode 16.
They usually send out an email a few days before the public release.