Why not just use the browser?

In the case of my bank:

I had to enable secure auth to access some features. This works only with the mobile app, even when logging on the web I need the mobile app.

Some functions are available only in the app as well. Now I’m stuck with the app because I need those and needed secure auth to access those functions.

It’s evil but I has no choice (no choice of other banks either for reasons I won’t go into here, just accept it and don’t tell me to change banks. Other banks are no better anyway. )

I need my banking app for 2FA to login with the browser. No, they don't use or allow TOTP.