Ultimately, I don't think the most important challenge is in binary firmware blobs, but the software which people depend upon to run their lives. What does it matter if you can run a completely free software stack on your phone, if your bank software (or your required government ID, as is looking depressingly likely) requires you to run a Big Tech approved phone OS? Perhaps the FSF can't do much about that, but that…
Use the website. I’ve never seen a bank where a mobile app is the only option for remote access. If my bank did that, I’d switch banks.
Also many websites are making it remarkably hard to not use the app if they even remotely sense you're not on an actual PC. FB and LinkedIn aren't banks but prime examples.