Hi @gianlucamichelini
Thanks for reaching out to us. I can understand your query. Currently, there is no such control in the Nav Menu widget that will allow you to show the Menu items in several lines. But, there is also a simple way to do that. You can simply make 3 nav menus on Appearance > Menus and apply those menus on the header by taking 3 EKit Nav Menu Widget. Please follow this screenshot for a better understanding.
Since the feature, you are looking for is currently not available on the EKit Nav menu Widget, Please add this feature on our feature request section. You will find the link to request a feature by navigating to the plugin details page. Scroll down to USEFUL SECTION and you will find the link named Request a Feature.
Let me know if you have any further queries or clarifications. I will be happy to help you.
Best Regards
Prosenjit