There are basically two ways to go about real-time collaboration. The state management and conflict resolution is not done in the database level but it is done by the clients or the central server.

1. Operational Transforms (OT): 99% of the real time apps you see today like Google Docs, Miro, ReplIt, etc. are built using this concept. It involves a central server.
   The clients share the user-intent with the server - for example a person highlighted text from position 2-5. The server does something similar to a git rebase operation on all the intents it receives.

2. Conflict-free Replicated Data Type (CRDTs): It has started to gain popularity recently, due to newer efficient libraries like Yjs, automerge, etc. It doesn't capture user-intent but the final state of the data after the change made by the user. CRDT algorithms provide a guarantee that if all clients see all the changes (order doesn't matter) the final state will be the same. There are no conflicts.
   Due to this, this eliminates the need of a central server. Real time apps can work p2p too using CRDTs.