I joined Signal and maybe 5% of my contacts are on signal as of right now. I don't think the critical mass is there yet, but I hope more people make the switch. I effectively cannot use Signal unless my main contacts are on it, which they aren't. The best thing I could do is try and convince all of them to move to signal so we can group chat on Signal instead, but it's a hard sell, despite the fact that most of the people I actively talk to are in tech or academia.

I think many people are probably fine with moving from Android messenger or WhatsApp, but it is going to be extremely hard to convince the Apple folks to stop using iMessage (or whatever they call it). Apple has also been working hard (e.g. green texts) to ensure that people stay on or convert to iMessage.