Why not just use a banking web site, which already exists In most cases?
The only real "service" that most banking apps offer that isn't available on a web site is photo deposit of paper checks. Paper checks are kinda last century and are rapidly declining anyway. Oh and privacy invasion --- an app makes it so much easier.
Nevertheless, using a banking app is very quick and convenient and is therefore used by many people. I don't see privacy education going that far, that people would abandon this convenience. Therefore I was wondering if an open source application would be possible here and bring the benefits that OSS usually offers in other circumstances.
It's used by most people because they've been taught to think "app".
Most people don't even know they have an alternative --- they don't know that they can easily make a link on their home screen to any web site that will look and function just like an app.
"Progressive web apps" even remove the browser interface so the casual user can't tell that they're not using an app. Chase; for example, has one.
It's also amazing how many developers don't know about PWAs and how they can be used to bypass the politics and extortion of app stores.
Would you suggest that rather than having discussions like my original question, we should better think about how to take different implementation approaches, thus circumventing several issues which come with 'traditional' apps?
The only reason PWAs aren't more popular is because app stores don't earn anything from them and they can't be used to data mine your phone.