Don't focus on just the files part. Spin it as here is your Team in Microsoft Teams, if you have it, or SharePoint Team site, with news this and here are you're files, and this is how you can share them with other departments while maintaining privacy to just your department on the files etc.
This is just my opinion but I've always gone the approach depending on your org structure, is having a Public communication SharePoint site for Each departments News and "Global" file document libraries, where files that should be available to the org are, for instance, HR's comm site would have benefits documents etc. in them, where the whole org has access.
Then you have a Private Team site for each department where their own files are, if they need to share the file to just a few people as exceptions you have the Share button to use.
This is usually the approach I take, sense you usually have Global drivers with no security, and each department has a folder, and another "Private" drive where each department can only see / access their own folder, these get moved into Private Department / Team sites.
This leads more towards Team area's and less about just Files and folders.
But there is another wrench here, where if you have a repeatable type of document repository such as projects, or customers where documents are consistent across the board but separated by an entity you start to use a central single repository and use metadata, so that finding these files becomes much easier. But I'm kind of going off normal standard network driver migrations as most of the time, the use case is how I laid it out above.
