If you think GrapheneOS isn’t private and secure, check out this comparison chart covering GrapheneOS, CalyxOS, IodéOS, /e/os, LineageOS, and Stock Android.
https://eylenburg.github.io/android_comparison.htm
It shows how much more GrapheneOS focuses on security and privacy compared to the others!
Edit: GrapheneOS only supports Pixel devices because they meet the project’s security requirements, offering hardware features like memory tagging (MTE), StrongBox keystore, hardware key attestation, pKVM, hardened malloc, and more: https://grapheneos.org/faq#future-devices