Support external photo library for multiple users

I’m running nextcloud (via docker) for my household, and want to share an existing photo library with everyone else. As background, there’s about 41k files, organized by year, month and then day directories, and this exists outside of Nextcloud itself. I have this directory passed in and known to nextcloud as an external storage named Photo-Library, available to all users.
What works:

  • All users have access to Photo-Library and can browse via Files app. There are no previews generated for anything.

What do I need to do to add all of these photos to the Photos app?