Owning a separate, dedicated piece of hardware for sensitive and critical activities (eg: banking) is a very good idea because it isolates them from all your other mundane, potentially risky activities.
Most people don't do this because of the various inconveniences and expenses involved, but if you can tolerate them it's about as safe as digital activities can get.
I had multitudes of non-smartphone based security devices in my life, cheap and dedicated small secure things, but those are endangered species now regrettably.
The banking apps still won't work. They insist on some signal from a SIM card "for my security," and I'm not willing to put a SIM card in a device that won't ever leave my house.
Why not a computer?
The banks are creating their own requirements for how to access their app.
Just like some users are creating their own requirements.
Both parties seem to be content to be apart of the problem and blame the other.
You might be fine having apps as closely tied to your real identity as your banking app on a device that's constantly collecting location and other data about you, but privacy is important to some other people.