Just start using Signal. Don’t push it for a reason for people who don’t care, just let people know “Hey, message me here”. The more people that use it - the better for everyone - whether they benefit or not.

The second part of that is use things like WhatsApp less or not at all, but you can always start with the first part. Maybe you already have folks on signal, and you can just start messaging them there until more folks come over.