I am opening this based on discussion on #2692 to look at the error messages as a whole.

There was a valid point made that the AMP cannot be enabled because this post type does not support it message is a bit confusing when AMP support has been deliberately turned off for the post type. The message is shown for all users, not just admins.
As a regular author, I don't necessarily know what AMP is, nor should I need to know. It should "just work". Having a non-actionable notice there doesn't make sense.

It's the same when a theme explicitly declares AMP support, as you get a Your site does not allow AMP to be disabled warning in that case and there's nothing you can do. As a user, I would not want to see any message at all there.

Related: #2702.