Deprecated call when deactivating

While trying your plugin, with DEBUG ON (PHP 7.4), I get, when deactivating it whereas image module was loaded with Fast rewrite:

PHP Deprecated: Non-static method WPPP_Dynamic_Images::flush_rewrite_rules() should not be called statically in /my_wordpress/wp-content/plugins/wp-performance-pack/wp-performance-pack.php [...]

As you can read, it’s because of:

public function deactivate() {
  if ( $this->options['dynamic_images'] ) {
    // Delete rewrite rules from htaccess
    WPPP_Dynamic_Images::flush_rewrite_rules( false );
  }

My workaround was to add the following static function inside class.wppp_dynamic_images.php :

	public static function static_flush_rewrite_rules() {
		// init is called prior to options update
		// so add or remove rules before flushing
		global $wp_rewrite;
		if ( $wp_rewrite && isset( $wp_rewrite->non_wp_rules['(.*)-([0-9]+)x([0-9]+)?c?\.((?i)jpeg|jpg|png|gif)'] ) ) {
			unset( $wp_rewrite->non_wp_rules['(.*)-([0-9]+)x([0-9]+)?c?\.((?i)jpeg|jpg|png|gif)'] );
		}
		flush_rewrite_rules();
	}

And modify accordingly wp-performance-pack.php by switching to it:

public function deactivate() {
  if ( $this->options['dynamic_images'] ) {
    // Delete rewrite rules from htaccess
    WPPP_Dynamic_Images::static_flush_rewrite_rules();
  }

Just to share with you.

Great plugin by the way ??