The DigiD app isn't required. You can log-in with DigiD using SMS 2FA. This is what I currently do, because I don't want to install closed-source software on my device.
I run GrapheneOS as a daily driver and slowly removed all proprietary software from my device by looking for FOSS alternatives on F-Droid. Luckily, I'm able to access banking and government in a web browser on a dedicated profile.
I do have a second Android device with a stock ROM that I keep turned off in a drawer in case I ever need to use an app that requires Play Integrity in an emergency.