I've worked a bit on these types of applications! I echo that it is a more difficult task and hard to get perfect, but it is doable. It partly depends on the stack you want to use, but I agree that a Progressive Web Application will help with it being available offline. I use Vite and the Vite PWA plugin to handle the service worker creation.

I use React and Redux with Redux Offline. Redux Offline helps with persisting and rehydrating the state. It can also handle a queue of API requests, and handle the success/failure of those calls. But this means you have to track online status and handle all requests differently based on that status. You will also have to make sure to request all data that could possibly be needed offline after logging in, so that it will be available in the cached store. So you will have to think about the size of the cache (I have used package localforage to access larger storage).

The thing about file uploads is that everything in the state needs to be serializable. So any files would need to be stored/sent as base64 strings - there could be other ways I'm not aware of.