If you need/want a robust multi-user experience, specifically with private personal library support, then Photoprism isn’t going to work, unfortunately.

• Free:
  • You can create multiple Admin users in the free version, but they all can see and delete everything (unless you don’t give Photoprism delete access)
• Paid (Essentials or Plus)
  • you can create “User” users who can upload photos - but they still have access to your full library
  • you can create “Viewer” users who can’t see private photos (but they also can’t upload photos).
  • you can share links to albums that are viewable by anyone with the link

I’ve been using it single user and it’s been great, though I should add the caveat that I upload my photos to my server using Photosync and don’t give Photoprism write/delete access to my library, so no uploads come from it. I had been using Photosync for years before even hearing about Photoprism so it just fit very neatly into my existing process.

Multi user features are effectively paywalled and not technically FOSS due to not allowing commercial use, but roles are documented at https://docs.photoprism.app/user-guide/users/roles/ and there’s more info at https://docs.photoprism.app/user-guide/users/libraries/

If Photoprism Plus/Essentials features could work for you, but the ongoing subscription is an issue, then you should know that - unless this has changed - you can sub for one month on Patreon or Github, use the info they provide to upgrade to using the Essentials or Plus features, and then cancel the subscription. I still have an ongoing one but I didn’t connect it to my Patreon account or anything so I don’t think anything would change (except for me no longer getting support, if I needed it) if I canceled it.

I think if you pay them like 80€ per year or something.

Yes, but not really. You can have multiple users but not multiple libraries.