What Is RCS Messaging (And How to Get It)

Your info on Fi is wrong. All Android phones, as long as they're not dual SIM, have RCS using Google's Messages App. My wife and I use it every day on Fi between my LG V40 and her Galaxy S8+.
 
Your step by step for verifying RCS is incorrect. I have the PIxel 3 and Verizon. You go into settings and you do NOT go into advanced. Chat features is a stand alone section in the main settings view. From there you turn it on and have customizable settings.