But why? What is happening to the VMs that prevents it? Is it an API incompatibility? I would expect any 15.x VM created on any OS to have the problem then, but it's only when it's created on 15.x host OS.

FB16084148

My 15.5 VM was created on 15.5 host. I signed into iCloud under System Preferences I then signed into the same iCloud account in Xcode Ran the project/test again and logs do not show "Device registered" as I would expect :(

Side note: The user is experiencing this with Github Actions and their VM images that are ephemeral/on-demand. The user does not have VNC access for example to sign into the apple account or Xcode, so the solution would need to support not having signed in to an Apple account, or, Apple to provide a way to enable a developer mode/sign in over SSH to the VM.