learndash_login_model_register_button_class

 <?php
/**
 * Example usage for learndash_login_model_register_button_class filter.
 */
add_filter(
	'learndash_login_model_register_button_class',
	function( $register_button_class ) {
		// May add any custom logic using $register_button_class.

		// Always return $register_button_class.
		return $register_button_class;
	}
);