They profile you by looking at you. Cop sees you use your grapheneOS phone and thinks you’re a drug dealer. There’s no tech involved. They just use it as a sign, same way they’ve used hoodies, skin colour, or nationality to suspect you of something.

Spanish police already profiles you for using grapheneOS

https://www.androidauthority.com/why-i-use-grapheneos-on-pixel-3575477/