I don't care if Apple goes 2 years without fixing this, but it's totally idiotic from App Reviewers to reject updates when this is a problem directly from Apple.

Holy shit I thought I was going crazy. Im having this exact problem. Going from iOS 15 Beta 2 to iOS 14.6 is showing this error and have no idea what to do. My Mac Mini M1 had macOS 12 Beta and then i restored back to Big Sur with Apple Configurator, but it also cant enable Find My, and that one is worse, it cant even show up in Find My page, the iPhone does show.