I've told the important people in my life that if they want to message me, they will need do it through Signal. It takes 2 minutes to set up, I show them how, and tell them that I won't reply to any SMS.

I've done the opposite: there's no way I'm going to install a messaging app, and everyone I care to interact with knows they need to either use SMS or email to reach me. Everyone's been perfectly fine with that.