So here's the thing, every time I try to move away from Facebook messenger I run into the same problem, nobody else in my friends or family actually want to use a secure, private messenger app like signal or telegram, my wife, my parents, my in-laws, my friends they're ALL on Facebook and they will never take signal seriously enough to actually use it, it really bums me out that there are these far superior options but without anyone else using them they're pointless..
Anyway what apps do you use to stay in touch with people?
My preference is Signal Private Messenger app, but like you, I have problems getting some friends and family to use it. So for the ones that won't, I just use Chomp SMS for my texting app.
The 20-80 rules applies here. Anyway, that is a strategy that works for me too.
The rest would be SMS. Sending files is links to my self hosted nextcloud.
Signal desktop is designed to be a stand alone app that uses the phone phone to first verify the connection via QR but after that relays messages, calls, erc direct from and to the server, inrependently of the phone app.
I think it was like that years ago. Or at least, it felt like it and if I recall correctly the Signal Protocol docs describe the functionality in that manner.