My grandma does not use any kind of phone, so it is going to be hard to get her to Element or Signal or anything.
However, my mother does use Element to talk with me and it wasn't that hard to help her download an app, tell her where to put the username and what is the name of the matrix server and quickly she was on her way to start a call and setup a room with the rest of the family where I share the pictures of her grandkids.
My users may not be nerds, but they are not stupid. They can learn.