Most of them don't support generic 2FA codes and sadly require some sort of proprietary app that talks to their servers. Setting them up usually also requires some sort of identification; think receiving a pin in the post. As far as I can tell, the only other option for me is to rent some sort of pin generation terminal from the bank which is, of course, ridiculously expensive.
ominousdiffusion
I don't think that it's the lack of quality hardware what is stopping adoption of Linux on phones. There are many resons why I don't consider someting like PostmarketOS viable as a daily driver for most.
First of all some apps are just not available on Linux. Banking apps are a prime example. Most banks are now requiring some form of app where I live and they don't even consider Linux. But that's also another problem in it self.
Secondly: driver support. Drivers aren't something one thinks about when talking about phones. But they are needed and mobile phones being what they are, most manufacturers aren't really open to do anything in that regard.
As an Android developer I'm also annoyed by the restrictive power management of Android. But it's there for a reason. On PostmarketOS my phone would be dead after sitting around all day doing noting. On Android I can maybe squeeze two to three days of use out of the same phone. And that's not even with the OEM rom.
That being said, I hope for a future were all of the current issues can be solved and we finally have a viable alternative to Apple and Google.
To be clear, I'm in no way trying to defend what Google is doing.
Yeah, I tried to use it as my daily driver a while back and what bugged me most was the terrible battery efficiency. Running the full desktop version of Firefox certainly didn't help. At that point the camera also didn't have any drivers. Since theres been some progress and we now have a work in progress driver for that model. Frankly it's amazing that this works at all and I'm incredibly grateful for anyone working on this.
I've actually been rather lucky and managed to convince most of my friends to join me on Signal so we barely need to rely on SMS anymore. But last time I checked there weren't any real Signal clients availabe for Linux phones. Of course, one could always use the desktop version but that still requires a phone to be linked to. Someone has managed to get the Matrix/Signal bridge working and rely on Matrix for the final delivery but that seems like too much tinkering for me :D