With offline first applications, you already have a realtime replication with the backend. Most offline first databases provide some concept of changestream or data subscriptions and with RxDB you can even directly subscribe to query results or single fields of documents. This makes it easy to have an always updated UI whenever data on the backend changes.

In offline-first apps, the operations go directly against the local storage which happens almost instantly. There is no perceptible loading time and so it is not even necessary to implement a loading spinner at all.

Offline-First is a software paradigm where the software must work as well offline as it does online. To implement this, you have to store data at the client side, so that your application can still access it when the internet goes away. This can be either done with complex caching strategies, or by using an offline first database (like RxDB) that stores the data inside of IndexedDb and replicates it from and to the backend in the background. This makes the local database, not the server, the gateway for all persistent changes in application state.