With my banking apps, the phone passcode won't get you into it. If Face ID fails it gives you the option to use the password for your online bank (Not your Apple password) and with the other it gives you an option for a PIN, but it's not the same or related to the passcode for your iPhone.
That's a good approach. Of course, if you use the keychain, while the passcode doesn't authenticate you on your banking app, a thief can access your keychain with your lock screen passcode....and then get into your bank.
And alas 2FA doesn't solve it because that SMS goes......right to your phone, and you can access your 2FA with that same Lock Screen passcode.
And if you got a little fancy and used email for your 2FA, that doesn't solve it either, since your Lock Screen passcode also opens your email there on your phone.
I guess the simple solution, until Apple stops forcing users to use the same passcode for the Lock Screen as for keychain as for almost every other OS level change on the phone is to not use keychain?
However, if you're like me you probably also access your bank account in the browser so if your account passwords are saved on your iPhone and they take over your Apple account, they have all your passwords. This isn't a security flaw in the banking app, but rather a security flaw in Apple's operating systems.
Yeah, I agree, Apple could mostly close this loop by allowing a different authentication be used for keychain versus the Lock Screen.
My concern about FaceID was a little different.
If FaceID allows access to your banking app, a thief doesn't need your special banking PIN to use your banking app.
They just need to go into Settings on the phone, and add their face to your phone. And all they need for that is the same screen unlock passcode they already have!
Then they back out to the banking app, and it lets them in with their face! They never needed your special banking app PIN.
Or at least that is how my bank's app works.
But this, luckily, is NOT required by Apple. That is, Apple allows the creators of the banking app to lock out all Face ID is the app notices that someone has added a new face to the phone's OS. That way, a thief cannot just add their face to the phone and use it to unlock an app that allowed use of the FaceID.
In such a scenario, the first time you try to use your banking app AFTER someone has added a FaceID to the OS, the banking app says "Nope sorry you need to use your app specific password before you can re-enable FaceID authentication as an option." Now, THAT is a smart way to code the app.
And I am sure glad option makes that an OPTION for app developers!
But it is not a mandatory feature, and, as I say, my banking app doesn't do that!!! So it actually means using my bank on a web browser may be more secure, or not using biometrics at all, or something like that.