> Good luck onboarding one's grandma to any of those.

Huh? Just do it. Install it, then help her if you have to, similarly to how you introduced WhatsApp (or whatever else) to her, for example. They may not like change, but if they are capable of using another piece of IM software, they are capable of using any of the mentioned ones.

I installed Linux for many people who have never seen Linux their entire life. On some occasions I explained how to do something, and that was it.

> Just do it. Install it, then help her if you have to, similarly to how you introduced WhatsApp

I think the point is that you don't need to help her for apps like WhatsApp, they manage to figure it out because it's simple enough.

Element, Briar, and Wire are very simple, too. You can use the same method you did with WhatsApp, even if it was just as simple as "Download X from the Play Store, sign up, login, and tell me what username you picked".

I as a tech user have had issues with getting WhatsApp to work. Much more than I have had with Element.

https://quicksy.im/ or just help her setup an account and install a client.