I have been successful in getting non-technical people onto Signal. As far as a technical product goes, Signal is kindof shit (among other things: no support for non-Debian-based Linux forcing users to use sketchy third party repos when they are a massive target for backdoors, really shitty UX for backups), but it gets the job done and seems to have robust encryption from what other people say (I am not qualified to evaluate this myself).

If a P2P solution that solved the aforementioned Signal issues were to have excellent UX, then that could probably work.

Lastly, what counts as "excellent UX" for technical and non-technical people seems to differ. For example, I consider Discord and Slack to be quite intuitive and easy to use, but multiple technical people have expressed to me that they find it to be very confusing and that they prefer other solutions, such as GroupMe in one example. To me, GroupMe shoving the SMS paradigm into something that's fundamentally not SMS is more confusing and poor UX, but to these non-technical people that seems easy. I suspect that Signal's shortcomings that I perceive are an example of this: making UX trade-offs that work great for non-technical people but are less good for technical people. I'm not sure what these specific UX trade-offs are, but I suspect that it's something akin to having a conceptually sound underlying model (like Discord or Slack servers/workspaces and channels), versus having really obvious "CLICK HERE TO NOT FUSS" buttons like GroupMe, while having graceful failures for non-technical users that can't even figure that out (like just pretending to be SMS in GroupMe's case if you can't figure out how to install an app, or don't want to put that effort in, something that many people know how to use).

This seems a bit more polished: https://tryquiet.org/

But some friction is to be expected.

My (very non-technical) 70 year old mom was actually happy to use Element because it has a nice desktop client, so she can more easily type and see pictures than on her phone screen. Simplex Chat would have worked for her as well.

Whet nerds perpetually don't understand, is that regular people hate the apps that nerds love, which are largely apps made by nerds who hate the apps that normal people love.