CryptOwlie RCS was working fine and effortlessly for me when I had my Pixel 4a. I had to upgrade it, due to it being end of life. I got a Pixel 7a and ever since I got it, it's been impossible to get RCS running on it. It seems to me that a lot of people struggling are using 6 and 7 series.
If Google has been making changes to RCS, which I believe they have, then RCS having worked before on an older phone may not be relevant.
Note that most GrapheneOS users are probably 6-series and 7-series users because:
- the 5 series is just about EOL;
- the 8 and 8 Pro are new and expensive;
- unlike the 6 series and 7 series, which have three models, there isn't an 8a yet(?).
Also, I think I saw Reddit complaints about Verizon RCS by non-GrapheneOS users on non-Pixel phones.