new iPhone suddenly messages stops working on MacPro
Asks for sign into iMessages
Messages are mainly sent through your phone. In certain cases, you can ask your phone to forward its messages to a specific Mac on the same Apple-ID. This sometimes takes some time to settle.
it is expected behavior that replacing your iPhone with a new one will cause all devices to have re-specify their connections, and have to sign in again. It may also take one or more Restarts of each device involved, and the passage of some time before it finally settles in and works.