SharePoint Online File sharing

[femina1970]

In SharePoint Online we are using a communication site . We have added subsites in the home page on the main menu. While sharing any of the folders from any of the site with external users they can read the files in the shared folder and get access to the main menu links as well. My concern is we are sharing only the folder with external users and they are not supposed to be able to access any of the subsite links. How to resolve this. Kindly advice.

[#2]

1. First of, avoid using subsites in SharePoint online. Use Hubsites and Connect the relevent sites to that one :) Subsites are a thing of the past, a real relic

2. They will only have access to the folder you share and nothing else. Subsite inherites from the main site but the mainsite doesn't inherit from the subsite

[#3]

Thank You for your prompt response.
I would like to clarify that our portal home page is a communication-hubsite .https://(Domain Name).sharepoint.com/site name/SitePages/Home.aspx
The sites linked in the main menu are also communication sites https ://(domain name).sharepoint.com/(site name)/sitepages/home.aspx
This is my portal scenario and whenever we are sharing the folder the external user gets the main menu .
We make sure that the folder has unique permissions (always stops inheriting permissions).
We have more than 5000 users or employees .in the sites the scenario is site visitors everyone folders unique permissions. please have a look and kindly advice