My family has a signal group. I started it two years ago.
Almost no one pays any attention to it, unless they accidentally open the app once a month, but they're all still there and can be spoken to.
I put a PSA out a month ago that I'll no longer respond on Facebook Messenger or SMS after the turn of the year. Tough shit. There was some groaning but, if there's no other way, either use Signal or invest in a Pigeon coop and get training.
RCS is shit, with SMS at least my phone comes with a messenger and I can download one from F-Droid. With RCS only one proprietary app supports it and it functions weirdly on GrapheneOS. In its current state it's practically a downgrade at this point and considering how bad SMS is that says a lot.