> They do not block unupdated phones because that will force users to buy exceptionally expensive devices to keep updated.

Hardly true, if they permitted Lineage and so on.

> Just like any enterprise software, it targets a set of common devices so they can provide support and QA on it.

Not really, there are a myriad of devices and they're not testing on all of them. A "pound sand if you're on an unsupported device and it isn't working" policy would be perfectly acceptable, as long as the issue isn't directly caused by the developer purposefully breaking the application for a subset of users that fail Play Protect check or whatever.

If any of what you were saying were true, then this wouldn't be just a discussion about banking software all the time, and we would see it happen with all kinds of other software, scaling with the complexity of the application or the level of provided customer support or the intended sophistication of the user or how "enterprise" the target market sounds... but none of this is the case, and if you tried to cluster products that do this along some axes the ones that stick out like a sore thumb are all of the form "controls something sensitive": money (banking, payments, investing, etc.), health data, copyrighted media (streaming), and multiplayer gaming (due to cheating issues). All of these people are very open about why they think they do it, and while we know they are incompetent, they are not doing it to be malicious and they have no incentive to lie to you about this: if a bank were truly not supporting your device because it was rare, they'd just say it, and we have ample evidence of this from banks choosing to not support "niche" browsers (including an era of "anything other than IE6" omg ;P). So: "cool story bro", but it is clearly wrong, lol.