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
In all my years of not using WhatsApp this has never happened to me lol. At best I've gotten some people to message me individually on Signal but not entire groups