I honestly don't care about apps. I switched to GrapheneOS and opted to not use Google Play Services, so my app selection is very limited, especially for things like banking apps. It turns out I can just use the website for the vast majority of them, and I can fill in the gaps with FDroid apps.
The main things stopping me from using a Linux phone (eg PostmarketOS) are:
- MMS compatibility - I use this a lot with family, and getting everyone on Signal or something isn't going to happen
- battery efficiency - the best I've heard is 8 hours with light use, and there are still issues receiving notifications in standby mode
- hardware quality issues and drivers - every phone supported by PostmarketOS either has a bunch of unsupported hardware (ie no camera support), or the hardware is poor (ie the PinePhone has crappy audio)
I don't need a flagship with top tier driver support, I just need basic phone things to work. I'm even okay with poor camera quality, provided I can take pictures of things and clearly read the text later. I don't need much in terms of app support, and I'm willing to help port things I need. But my phone needs to work as a phone, and it needs to do so all day without needing to charge until night.