chenxiaolong Just another confirmation post: I've tried this on and off over the past few months and this is what did it for me (Pixel 8 on MEO Portugal). I've been running this for the past week with no issues to report.
For the record, I have a Xiaomi Redmi Note 7 running LineageOS 21 and RCS worked immediately, even while failing SafetyNet / PlayIntegrity, so I have a suspicion that this is not a anti-root measure, but something else on Google's end (as some of you have pointed out already)