"debugger vendors in 2047 distributed numbered copies only, and only to officially licensed and bonded programmers." - Richard Stallman, The Right to Read, 1997
I only have Linux PCs (laptops) and servers, 100% of my work and personal stuff is done there (though for work I do need to hop into MS365, Google Workspace, Zoom, etc, hooray for browsers, my final firewall between me and the walled gardens, though we can have a whole discussion on that).
For mobile, we have PostmarketOS, Phosh, Ubuntu Touch. I really must try living in them, is it on me? IDK, our government even has an identity app for iOS and Android. I should not be using it, I should stick to web. But its so much more convenient. I'm just weak, aren't I?
Maybe I should go for Ubuntu touch, with an iPad on the side or something. At least my most personal device is something I control then. Or just keep my Linux laptop handy (or make a cyberdeck!). But I want a computing platform that does not require carrying a bag. It's kinda sad. Even GrapheneOS (one of the most personal and secure mobile computing experiences out there)'s future is in the hands of its greatest adversary, the one that does not want you to have a personal computing experience.
This is not too hard. What is hard is to trust it enough. A FOSS OS, by definition, allows to install whatever software, and allows for modification of itself. It is built to overcome limitations, not impose them. In this regard, it's a perfect tool for a criminal who wants to circumvent security measures, because these are limitations. It's the same problem as with cheaters in online games, only with more than games on stake. Banks and payment systems want guarantees of integrity and protection, including protection from user's actions.
A FOSS OS also assumes that the user values the freedom, and is competent in its technical aspects. This is emphatically not true about many users. They choose iOS because it's locked down and thus they cannot inadvertently do something they don't understand, and can't be bothered to learn. More importantly, their grandmother cannot do something she doesn't understand but scammers persuade her to do.
It's a bit like driving on public roads. If you want to drive yourself, you have to reveal your identity and obtain a license. If you want the hassle, take a bus, but buses only go along their routes. Letting unlicensed people drive cars where they see fit was found unacceptably dangerous for everyone eround. Maybe mainstream mobile software development will follow this model, too :(
At least for now.
I'm not aware of any major issues this has caused.
The trust isn't the issue. Google and Apple has made DRM easy for these companies to integrate, and therefore they do it. There isn't more to it than that.
Decades of desktop malware used to drain bank accounts are not a major issue?
In any case my bank has not banned the use of Linux to do homebanking. Why? Because there isn't a easy to plug-and-play API to do DRM and remove consumer rights. This is largely for historic reasons, but there is no reason a FOSS mobile OS couldn't work.