Banking apps are the deal-breaker for me. I only do business with banks that offer alternative ways of securing transactions e.g. eTan / ChipTAN / PhotoTAN with a separate reader / generator (see https://www.bsi.bund.de/EN/Themen/Verbraucherinnen-und-Verbr...). This is probably a pretty European thing to do, but at least it avoids being locked in and being tracked.
I did that too (in Austria) for a long time. Fortunately my Bank (Erste Bank / Sparkasse) fully (almost fully, no nfc pay, since it depends on GPay) supports GrapheneOS now
I'm happy that my bank (still) allows me to have both a stand-alone reader and a mobile app to authenticate. Because if you lose your authentication device, a lot of things suddenly get a lot harder.
I also tried to use an old phone as a backup device. However, most authentication apps only allow it to be installed on a single device.