Depends on the application, naturally.

Most of them, even if native don't really work without the API based backend.

If we take out the garbage apps, copycats, and games without DLCs, most stuff is some variation of form over data.

And those that are really special, needing native APIs, working offline by default, can probably be reduced to about 10% of apps.

A website can work offline, too. Service workers are a feature that any website (installed or not) can use to (pre)cache assets, etc. On iOS, that data will get evicted if the user doesn't visit the site at least every 7 days, though. Other platforms keep the data for a lot longer, but will evict at some point, too.