Matt, can you clarify? You wrote "Starting in iOS 15, iPadOS 15, tvOS 15, and watchOS 8 the system requires the new, more secure, signature format that uses DER to embed entitlements into your app's signature." However https://help.apple.com/developer-account/#/dev2ab310a57 says "In iOS, iPadOS, and tvOS 15 or later, some entitlements without “com.apple.developer“ in the entitlement key may require the DER-encoded version to be included in the provisioning profile" -- which is not the same thing. The official docs are too vague: some entitlements ... may require? We need a complete list of the new requirements, so someone can inspect a given Provisioning Profile to determine compatibility with iOS 15, without having to test an install. My company supports customers who sometimes have literally 100's of in-house apps, and asking them to test re-installing each one -- with only a few weeks before iOS 15 drops -- is not feasible. Also, earlier you had mentioned official documentation was still forthcoming. Is the help.apple.com link above what we were waiting for, or is there something else we can refer our customers to? Referring them to a developer forum thread seems a bit sketchy.

Answered at https://stackoverflow.com/questions/63267897/building-for-ios-simulator-but-the-linked-framework-framework-was-built