I've been using Signal for years, precisely because of WhatsApp and Meta and what they really stand for. Kids (adult) and family are all on it because of me.
Initially, I was the only person who used it, but I refused to used WhatsApp and got four of my friends (who were the only real group chat users I was interested in talking to) to use Signal. We all regularly use it, even though they are all on WhatsApp. They know my ethical objections to WA and Meta. Every Friday there will be a group call - even though we're all on iPhones now (I was on Android for many years).
One in particular takes the mickey out of me for it sometimes because he says "What difference are you making? One Person? Makes no odds."
But it -does- make a difference. A tiny one, maybe, but it's something that has been worth making the effort for. I think it's important to tread the right line between expressing why you're doing it and not making yourself unpopular but I think it's an important thing to try to do.
And now if anyone asks if I have WA I just say I don't use it, you can either text me or use Signal. I have probably 20 contacts on there, and anyone who I have meaningful connections with uses Signal. Once installed it's basically zero friction for them, they just find me there instead of WA.
I know network effects are massive, and it won't shift any time soon, but I think it's important to draw an ethical line in the sand, and it's something I decided to do a long time ago. One guy gave me a WA ultimatum and I just said "OK, but that's not for me, I'm not using it", and that was that for about a month. Then he installed Signal.
Any business that communicates via it I express my preference and if they insist that's how they message (had this with an insurance company!) then I say I won't use their business any longer.