SyncedStore is a brilliant Yjs reactive store for SPAs, it’s not a database. It like an automatically distributed real-time reactive redux/vuex for collaborative apps.

The y-IndexedDB you linked to is actually part of the Yjs toolkit, it is a way of persisting a Yjs document in the browser for offline editing in a PWA. It doesn’t provide a way to sync a whole (or subset of a) database like Couch/PouchDB does. It’s a very important part of the Yjs toolkit but doesn’t do what I’m describing (it’s just a key value store).