For real! One of the things that made using Signal a non-issue for me was due to it being able to use SMS as a fall-back and therefore didn’t need me to push friends to also install another message app. I really only first installed it because it was the messaging app my local chapter of the SRA was using. I was excited that it did the shit I loved about the old Google Hangouts before they unnecessarily chose to break shit back out into three replacements. Being able to use a more feature rich messaging service when the people I am messaging also have it is awesome. But being able to still send a basic SMS from the same app without leaving is super nice. It is the main thing I always envied about how iMessage has worked basically forever.
Fortunately some of my friends and co-workers also have needed to install Signal for similar reasons I did or for remote therapy stuff. But it is so hard to get others to just install it just because it is privacy focused and since we already have Facebook Messenger/Discord/Snap/IG/Line and of course SMS. Also hate feeling like I am being pushy or annoying unless I am directly asked about apps to try or some specific reason.
I also have fond memories of using Gaim/Pidgin back in the day for being able to just have one IM client that could work with basically whatever any of my friends/contacts liked using. A universal chat/message client really seems like something that would be cool to see come back.