WhatsApp & Pinephone - What are the alternatives for collaborative comms?

[danimations]

I have a problem I hope someone can help me solve.

I have a Pinephone and a client that I work with has asked if I can install a WhatsApp client on my phone in order to keep up with some group discussions there about a collaborative project. I've never used WhatsApp on any device, and after learning that it was bought by Facebook a few years back, I'm disinclined to use it.

I looked into the practicalities of setting up WhatsApp on Pinephone anyway, using an in-browser or stand-alone desktop client... and there's a major problem. You need to already have WhatsApp installed on an Android/Apple smartphone before your can set up a desktop client on a PC (or Pinephone).

Is it possible to establish a Whatsapp account without using an Android or Apple handset beforehand/simultaneously?

Is there anything that the WhatsApp platform offers that alternative platforms don't?

My preferred solution is to encourage the client to switch to an alternative collaborative chat/file sharing platform that is private and mobile friendly, but I'd need to convince a bunch of people to change platforms. What alternative(s) would you recommend?

Any advice will be warmly welcomed.