That's exactly the problem that I tried to solve with the OS I'm working on. You can have a shared jellyfin instance if you want everyone to access the same library. But you can also create OS users, with their own jellyfin instance, and within that you can set access or only to certain folders. That only have the contents that you want them to access.

It's not as efficient as granting access within jellyfin, but it's pretty close to what you're trying to do.