> insistence on GrapheneOS is that by the time you are using Google's libraries, like Maps, Play Services, or their notification service (Firebase, IIRC), you've already lost.

Graphene offers the option of sandboxing Google apps should you want them. The usual setup is a second user profile with all the Google stuff in it. My main profile only contain FOSS apps and nothing passes through Google's servers. I use the Google profile for the maps with a dedicated account maybe once a month when driving somewhere unfamiliar.