Disable Gutenberg for Specific Post Type

If you want to use the Classic Editor for a specific post type, add the following code. For more on creating Custom Post Types.

add_filter( 'use_block_editor_for_post_type', function( $use, $post_type ) {
	if ( $post_type === 'your_post_type' ) {
		return false;
	}
	return $use;
}, 10, 2 );

Replace your_post_type with your CPT slug.