I just recreated the provisioning profiles (edit, rename, save, download) and then uploaded and it worked. Another thing, while I was having the problem before fixing it, I had a previous build in TestFlight which was built with the previous provisioning profiles, so I tried to release it. It failed and I got an email saying that the profiles are invalid. So it seems like a bot at Apple (either software or human) revoked something that was used to validate the profiles. One of the reports in this thread suggests that this was reverted.

I have the same problem. Setting the minimum deployment to 17 allowed me to install on my device (ad-hoc). Then I tried to build for release but the organizer won't upload with the same error: NSExtensionPrincipalClass is unexpected. So I removed NSExtensionPrincipalClass, recompiled and uploaded successfully. However when trying to install from TestFlight, it failed because NSExtensionPrincipalClass is missing. The console shows: "Appex bundle at /var/installd/Library/Caches/com.apple.mobile.installd.staging/temp.kfzF1C/extracted/Payload/.app/PlugIns/XXXWidgetExtension.appex with id com..***.widget does not define either an NSExtensionMainStoryboard or NSExtensionPrincipalClass key with a string value in the NSExtension dictionary in its Info.plist" So - with NSExtensionPrincipalClass - can't upload to appstore. Without NSExtensionPrincipalClass can't install because it's missing. What's the deal!?

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There's a similar thread here: https://forums.developer.apple.com/forums/thread/732892 It didn't help me. What happens to me is that if I define NSExtensionPrincipalClass, the organizer won't let me upload to AppStore because NSExtensionPrincipalClass is unexpected. If I remove NSExtensionPrincipalClass, TestFlight fails to install because NSExtensionPrincipalClass is missing...

There's a similar thread here: https://forums.developer.apple.com/forums/thread/732892 It didn't help me. What happens to me is that if I define NSExtensionPrincipalClass, the organizer won't let me upload to AppStore because NSExtensionPrincipalClass is unexpected. If I remove NSExtensionPrincipalClass, TestFlight fails to install because NSExtensionPrincipalClass is missing...

@eskimo , we were authorised to use this entitlement since iOS 14, and I already made sure it's selected into all our proivisioning profiles. It was working for us perfectly until now. It just stopped working with Xcode 15. I suspect a bug in the new upload tool.