Use internal helper function to determine if post type is supported.

includes/utils.php

@@ -45,7 +45,7 @@ function is_using_gutenberg( $post ) {
 	}
 
 	// Make sure this post type supports Gutenberg
-	$use_block_editor = use_block_editor_for_post_type( $post->post_type );
+	$use_block_editor = dt_use_block_editor_for_post_type( $post->post_type );
 
 	/** This filter is documented in wp-admin/includes/post.php */
 	return apply_filters( 'use_block_editor_for_post', $use_block_editor, $post );
@@ -952,7 +952,7 @@ function dt_use_block_editor_for_post_type( $post_type ) {
 
 	// In some contexts this function doesn't exist so we can't reliably use the filter.
 	if ( function_exists( 'use_block_editor_for_post_type' ) ) {
-		// Filter documented in WordPress core.
+		/** This filter is documented in wp-admin/includes/post.php */
 		return apply_filters( 'use_block_editor_for_post_type', true, $post_type );
 	}