Yup. I started using it in part because of his tweet

Yes, but then last year he started saying it had known vulnerabilities that weren’t being fixed, around the same time Telegram was attacking Signal’s credibility. I seem to remember him outright endorsing Telegram but have only done a quick search and that hasn’t popped up.

4years ago yeah https://mashable.com/article/elon-musk-signal

Not really. It’s still not big. It definitely got bigger after he supported it though.