I understand that it may be problematic sometimes but this was very smooth. I didn't even say anything.
A: what's your number for the whatsapp group Me: I don't have whatsapp because of facebook. B: ok, we have to use signal then A: ok
And that was it. Life can be very easy sometimes
Still, you were lucky that your colleagues are aware of alternatives and will use it (I hope). I wonder though if people will migrate because of you. Its tough to encourage others to communicate Signal while majority use Messenger or Whatsapp. Their reasoning for that is the most friends and family member are on mainstream solutions.
Signal is an interim solution imo for most people, which I also recommend. Not too extreme, not to "geeky", which introduces them to alternative app world.