Options of a hybrid application

I am working on a project that some of its users might be online like 30% of the time because they're mobile. It consists of a central database, one Api and one UI. If we're going completely with web design architecture it would be simple, a VueJS UI attached to a .net core Api with a SQL database. But because of the offline users we're looking for alternatives. These are the options we have, I would appreciate any input on this. Some conditions to consider:

1. We can install app on user machines, but we prefer not to because we need to maintain installation, updates, sync, etc.

2. The project complexity is medium. Perhaps 5-10 forms to be filled up and some basic calculations and image uploads from client side to be pushed to database.

Options we have thought of (In addition to the main web site):

1. A desktop app that runs and talks to the Api when is available. When offline it would store on local database and sync when back online again. This kind of sync from experience is very hard to implement and maintain.

2. A locally hosted website that runs on local IIS, and the Api would talk to the main Api when online, but store data on local db when offline. Again, we have to deal with sync. The only benefit of this is that we won't need to invest on development of a site and desktop app together. But now updates are even harder.

3. Electron. Would be a good solution here, but it is not mature enough and we are evaluating if it would be a risk.

4. Xamarin. gives us more flexibility, but still it's considered local app.

Any suggestion is appreciated :-)