GrapheneOS is more secure than the factory Android load on Pixel phones, but Ingress refuses to run on it.
Per Play Integrity API and Future of GrapheneOS - GrapheneOS Discussion Forum, GrapheneOS passes the hardware attestation API, is not rooted, and does not use an unlocked bootloader.
Ingress should run on it.
See also Attestation compatibility guide | Articles | GrapheneOS.
Edit: thanks for closing the topic so I can’t reply to you.
It went about as well as I’ve come to expect from the Ingress player community, with responses ranging from “tough ****” to a personal attack, and with no response from Niantic.