Cannot access protected property Joomla\CMS\Menu\MenuItem::$params

Hi.
We have checked and fixed that issue on your site.
Now you can save the module.
Please recheck it.
Regards.

Hi.
The issue form our source code. It get the virtuemart product to the menu items. When you have a lot products, it can't save to the module params. We have disabled that function on our module to avoid that issue in the future. We will release a new version to fix that issue.
Regards.

Yes, if you need help, please let us know again.
Regards.