You talk of what you don't know. Bank apps here are mandatory by law. If you don't or can't use a bank app then you can use a SMS verification approach where you are required to PAY SMS that the bank sends you.
Receiving SMS here is free, only those from the bank for verification are to be paid without the bank app, it's just a scam to force you to use the bank app.
The bank app itself is not a scam like a you are the service approach, and it's not free either as you pay the bank services with your bank account fees already. Maybe you don't pay a specific fee for the app, bit you already pay your home banking fees anyway.