Yeah! I hear you, especially regarding 'onboarding' often being a barrier. (Thankfully, Signal is bloody easy.)
My own attitude to family and friends is to say, "If ya wanna communicate with me, these are the acceptable options..."
If they don't wish to use appropriate methods, that's fine, but they can't message me. Bugger 'em!
I encourage the use of Signal as a 'gateway drug"... I mean, "app," and several people have subsequently added other private messaging apps as options.