>banks and the like have a say in how I choose to access their more convenient services

I disagree. I don't understand how it's fine that I can access my banking services with my Gentoo machine, with everything compiled from source by myself, but it's somehow a problem when I'm not using either Apple or Google certified OS on my phone.

I'm sure they want to prevent the first scenario, like various streaming cartels already do, but I hope something like EU throws a fit if they do.

What kind of actions can gentoo do with your financial accounts, and what levels of user authentication does it use to do it? My phone can effectively act as a bank card with contactless payment or I can transfer up to a daily allowance (that would be painful to me if it was misused) of thousands with biometric auth. Similar to the OS if you're doing that with any browser with a web login you could potentially compile it to behave how you like or lie about what it's doing

Because it's a bank there's going to be insurance behind the scenes to cover them if something goes wrong, and I assume part of that is ticking off enough points to be confident a transaction is secure or different payment limits on confidence levels.