There is only one banking app I have that does not fill my iPad screen, Monzo. Every other one either makes a cross device compatible app that sizes well and handles screen rotation for landscape or an iPad specific app.
If you write for iPhone you write apps that size correctly across the varying screen dimensions of the different iPhone models, to add iPad your just adding one more model, plus a flag or two to show ithe app works on both device types. Being specific, taking into account iPad Pro, there’s more than one model, but I’m only singling that out for the more pedantic readers.
There may be reasons not to share the same app, in that case you write an iPad specific variant, bringing most of your iPhone code over and changing whatever it is you need to based on your decision to have two apps.
Also, why the heck, even if I have to use the iPhone app on my iPad, can’t I log into both, instead of that ridiculous email check, every time, I swap device, no one else does that. If I genuinely authorise two devices…just accept that!
The same is true, in fact more so, for Android devices, because there are SO MANY screen sizes for Android, an Android app should size to any screen dimension as best it can. (A minimum size obviously, but that normally isn’t an issue)
So how about it?