Use only one user on multiple devices


I am trying to make an app, first iOS then Android, which will have synced offline-first realm.
Idea is to make changes in database through Realm Studio, and for all devices to sync with them when they have internet access.
The user will only read from realm, without need to do any writing. Can I create only one user, and use it on multiple devices, or should every new device register, let’s say with anonymous credentials, a new user?
Problem is that when device logs in with anonymous credentials, realm syncing does not work.
Concept of let’s say thousands of devices logged in with a single account does not sounds good to me, but I can’t find solution to that.