Easy, don’t use digital technology and live in a shack in the middle of Bir Tawil. That’s the exact attitude Apple, Google, et al. want people to have.
Privacy is not a game of absolutes. You make a threat model and do the best you reasonably can. I hope you at least enjoyed your head start on privacy by choosing GrapheneOS.
If you have $150 to spare (depending on country), a secondhand Pixel 7a is a great starting point to try out GrapheneOS without directly contributing to Google. Just make sure it’s carrier unlocked so it allows bootloader unlocking. For $100 more, a Pixel 8a will get you several more years of software support. Practically everything just works with GrapheneOS.
Fairphone with /e/OS is leagues better than Googled Android, but little to no additional security hardening has been done over plain AOSP (which itself is quite secure against non-state-sponsored attacks to be fair). Also, some pings to Google have yet to be patched out, see https://eylenburg.github.io/android_comparison.htm
Linux phones are much better than they were a few years ago, but unless your workflow tolerates the occasional disruption due to a bug or missing feature, they aren’t exactly production-ready for most users. But a good sneak peek into the future of privacy phones given the way Android is headed now.
MicroG works for many things, but not everything. Google’s own apps don’t play well and some of my work apps don’t send notifications when using MicroG. But GrapheneOS supports a sandboxed, proper instance of Google Play Services should you need it.
Google Wallet and anything requiring the Play Integrity API will not work with third-party OSes, not even GrapheneOS (perhaps until they release their own phone).