A family of Microsoft on-premises document management and storage systems.
if I remember correctly structural navigation doesn't use security trimming OTB. I.e. users will see all sites but when will click on those where they don't have access they will get Access denied.
In order to hide links for groups of users in global navigation target audiences can be used: Target navigation, news, files, links, and web parts to specific audiences. The idea is that you set target audiences for links in top navigation (e.g. using Sharepoint groups) and these links become visible only to users from this SP group (and won't shown to users from another SP groups).