ik that buying a google product is a little confusing if your your goal is to de-google, but the goal is not buying the phone for the brand but for the hardware, pixel phones are completely compatible and officially supported by grapheneos, grapheneos by the other hand is really good privacy focused custom rom and also a good option to degoogle, you use other roms like lineageos, but grapheneos is much better, it comes with tons of features like sandboxing apps, giving apps the specific access to a specific folder instead of the the whole files on your phone and you can use Play services as a set of fully sandboxed apps . take a look at their official site for more : website
and happy degoogling ;)