GrapheneOS will sadly stay unaffordable for many.
The most well-known: https://wiki.lineageos.org/devices/
You can’t use stuff like banking apps on a modified device and losing access to normal android devices would be a big blow to the momentum of the F-Droid community. GrapheneOS might not be a big enough community to sustain work on the projects delivered by F-Droid.
IME such apps are few and far between. The most trouble I ran into is play store refusing to show apps because they claim the app isn't compatible with the device, but that can be worked around with aurora store.
And Google has an answer to the "just install the APK from somewhere else" workaround, too. Many apps now integrate a check that prevents them from running if they're not properly linked to the Play Store.
I had an app that I needed to use, and the only available log-in method was via firebase's SMS. Firebase flat out refused to allow me to login because of Google Play Integrity, and there was no web only option.
I ended up having to use my spouse's iPhone...
>Firebase flat out refused to allow me to login because of Google Play Integrity
Sounds like the issue is that you don't have play services installed, rather than play integrity specifically.
Cumbersome, but any other deterring reasons why "not a good workaround"?
For me it seems the opposite - if these "normal" (GMS spyware) Android devices lose the access to F-Droid and it will only be possible to install malware/adware from Google Play, then maybe that will push more people to value unlocking the bootloader..