A fatal PHP error is occurring when attempting to add new posts with instant indexing enabled on the new version.

PHP Fatal error:  Uncaught ArgumentCountError: Too few arguments to function RankMath\Instant_Indexing\Instant_Indexing::before_save_post(), 3 passed in /wp-includes/class-wp-hook.php on line 307 and exactly 4 expected in /wp-content/plugins/seo-by-rank-math/includes/modules/instant-indexing/class-instant-indexing.php:262

This is due to the update argument not being passed. Changing the following code:

public function before_save_post( $data, $postarr, $unsanitized_postarr, $update ) {
	if ( ! $update ) {
		return $data;
	}

to

public function before_save_post( $data, $postarr, $unsanitized_postarr, $update=false ) {
	if ( ! $update ) {
		return $data;
	}

Should stop that error from happening.