try-disabling-amp-by-default.php

<?php
/**
 * Plugin Name: Try Disabling AMP by Default for a Custom Post Type
 */

namespace Try_Disabling_AMP_By_Default;

const POST_TYPE = 'book';

add_action(
	'init',
	function() {
		register_post_type(
			POST_TYPE,
			[
				'label'  => 'Book',
				'public' => true,
			]
		);
	}
);

add_filter(
	'amp_post_status_default_enabled',
	function( $default, $post ) {
		if ( POST_TYPE === $post->post_type ) {
			$default = false;
		}
		return $default;
	},
	10,
	2
);