I talk to a LOT of people about plurality stuff, and there's a reason I always lead with "I have multiple personalities." Even the diagnostic term MPD or DID has very good odds of just getting a polite (baffled) smile and nod, "multi" is outdated and nobody seems to use it but me, and "plural" is still rarely used unless you're already in the bubble. (I am having to find a roommate again, and I REALLY have to hammer on the "I have multiple personalities" thing because just saying I'm plural is meaningless to them and so their brains totally gloss over it, or assume it means polyamorous.)

The echo chamber effect of online makes it seem like the words are more common than they are, but I assure you, once you are out of the echo chamber, nobody knows wtf you're talking about. At least in my experience.