Hi
Yeah, your demo is broken too but different. Check it on:
https://validator.schema.org/#url=https%3A%2F%2Ft4-framework.demo.joomlart.com%2F
In our case we use separators so we get:
name HELP & CONTACT Support CentreFAQsContact Us [this is what happens to separator, all child items are listed]
name Support Centre [child item]
name FAQs [child item]
name Contact Us [child item]
And we should get at least:
name HELP & CONTACT
name Support Centre
name FAQs
name Contact Us
But even then this is not a proper Schema "SiteNavigationElement" as for each, non-separator, menu item you should list URL next to name to. To do that I think you would need to go with a list. Something more like the example at https://www.rankya.com/structured-data/structured-data-examples/
We have edited "t4-plugin\themes\base\html\mod_menu\mega.php" and removed your implementation of Schema "SiteNavigationElement" as it might cause more harm than good.