You don’t need a Pixel to get off the big-tech system, and not many people will be able to help you with an iPhone; if it’s even possible. You can install a variety of custom Android OS on plenty of devices besides Pixel- and it will take Google out of the drivers seat (depending which distro you choose and if you still want to use Google Play services).
But a de-googled Pixel running Graphene OS is the cream of the crop when it comes to security, privacy, and hardening of your device at this stage!
GrapheneGoat created a great post explaining in short how de-googling works, and just how secure it really is. Graphene OS DIY De-Googled Phone Explained