RCS just stopped working for me also. Messages settings says RCS is on and "connected," but all messages are reverting to SMS.
It has always worked fine for me since I first installed GrapheneOS almost two years ago. Initial setup was fast and easy and I've never had a problem since. Although, I've never been able to get it to work on my partner's phone, which I put GrapheneOS on a few months ago. Maybe I was grandfathered in, as it were, from a time before Google got so picky about all of the verification checks for enabling RCS?
But what is the point of this. Why make is so difficult? Why doesn't Google want anyone to be able to install Google Messages and use RCS? Is there a future in which it just works, like SMS?
That said, does anyone still have RCS working?