Hi @MD ,
To manage user permissions for a SharePoint Online hub site and its associated sites, it is recommended to use SharePoint groups. You can create SharePoint groups at the hub site level and add them to the associated sites as needed. Additionally, you can create custom permission levels for the SharePoint groups to provide more granular access control. When users change positions, you can simply add or remove them from the appropriate SharePoint groups instead of managing their permissions at each site. It is not recommended to use nested security groups as they can cause performance issues.
It is also important to note that managing permissions in SharePoint Online differs from managing permissions in on-premises SharePoint. In SharePoint Online, permissions are managed through Microsoft 365 groups, which are automatically created for each team site. Communication sites, on the other hand, use the standard SharePoint permissions groups (Owners, Members, Visitors).
It is not necessary to switch from modern to classic experience to manage user permissions in SharePoint Online. Instead, it is recommended to use SharePoint groups and custom permission levels.
For your references:
https://learn.microsoft.com/en-us/sharepoint/planning-hub-sites
https://learn.microsoft.com/en-us/sharepoint/modern-experience-sharing-permissions
https://sharepointmaven.com/how-to-sync-hub-permissions-to-the-associated-sites/
Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.