The only thing you can do to retain some level of privacy is find a phone with great lineageOS support, install with no gapps, install fdroid as a system app so

The only thing you can do to retain some level of privacy is find a phone with great lineageOS support, install with no gapps, install fdroid as a system app so it can manage updates. You still won't get kernel updates when security issues come around because not even the OEM can update that without convincing all the vendors to update their blobs.