Try Delta Chat, it's even more like email but for chat (it runs off off Chatmail relays, it's literally email but for chat).

But more importantly it's easier to use, I'd have to set my mom up on Matrix but on DC I just sent her the invite link, she downloaded the app and made an acct (and may have had to click the link a second time to get to me but still), it was easy as hell! Then next time we were together I had her open her phone and I set her up with a few extra relays for redundancy. And she actually uses it now! It's basically a whatsapp clone UI wise so I guess that helped, and at first she'd text me and I'd reply on DC until she started remembering DC exists.

My dad's a bit better, all I had to say was "it's encrypted" and he made an acct and hasn't used SMS with me since lol.