You can look for yourself cant you.
I cannot tell you.
This i know. But the majority will not move by itself. I told my fam that im no longer on whatsapp and if they want to get in contact they should either msg me through signal sms or just call.
I dont think its open source. But if foss is what you are after then this might not be for you.
Instead of whatsapp, fb messenger, imessage, go for skred
Skred is the first secured messaging app allowing total freedom: you don’t need any email address or phone number to use it. Skred is open. No subscription is necessary, there’s no operator, no SIM card and no tracking.
So i was on reddit and noticed skred was mentioned. I never heard of it and gave it a try.Its French. It has some nice features. Does not use a phonenumber.
Give it a try.