- Edited
I'm pretty sure RCS on Grapheneos is impossible at this point. "Google has begun implementing Play Integrity API attestation checks (popularly known as “SafetyNet checks,” inspired by the predecessor SafetyNet API) on the Google Messages app." Google spokesperson admitted they're doing this to "fight spammers."
https://www.androidauthority.com/p-3421652/
This is the same attestation that prevents things like Google Pay and some banking apps from working on grapheneos, right? If that's the case, RCS on grapheneos is dead in the water since grapheneos developers have said repeatedly that they won't play the cat and mouse game to get apps to work with this as it will take too much time and potentially erode security.
Articles are also pointing out that unlike Google Pay/Wallet that notifies you that it won't work on custom Roms, Google Messages doesn't notify you but silently breaks RCS functionality, even if the app settings say RCS is enabled.