In the Netherlands we have a system called DigiD to login into to most government websites like your taxes and city, etc.
When I contracted for the city of Amsterdam I learned they’ve been pushing hard for the DigiD app to two factor authenticate instead of text message, because of contracts Digid charges a lot per text message validation and none for app.
For example with bankID (sweden, and I think the norway version does the same) when you need to authenticate you either scan a QR code with the bankID app or select "on the same device" and then the website will interact with the bankID API to auth.
Either way you don't need your own app to get proper auth working with this sort of government login.
(With bankID the app devs still pay a per-auth price, but that is not due to any technical reason, just because its made by a profit-driven semi-monopoly)