My team is building a Sharepoint site as a document repository with many folder levels. We are migrating data from another cloud server and importing security access profiles using third party tools. The issue is that when users only have access to a certain level of folders, the navigation seems impossible since the top levels folders are not visible to them. I've included the picture below to showcase how would 3 users view a particular structure of folders given their security access levels.
Bear in mind we are talking about thousands of folders with lots of hierarchy breaks, and that the customer wants to keep the current security access profiles as is, as they can't afford to have any issues with confidential data being accessible.
The only thing that comes to mind is sharing each and every folder to each user who needs access. This will stink if you ever have user changes.
I did something quite like this but automated the membership updating with a strip/re-assign flow in Power Automate. You might build this logic by number of parent folders, by name, what have you, but it could be done. Not a fun script, though.