While Jitsi is open-source, most people use the platform they provide, meet.jit.si, for immediate conference calls. They have now introduced a “Know Your Customer” policy and require at least one of the attendees to log in with a Facebook, Github (Microsoft), or Google account.
One option to avoid this is to self-host, but then you’ll be identifiable via your domain and have to maintain a server.
As a true alternative to Jitsi, there’s jami.net. It is a decentralized conference app, free open-source, and account creation is optional. It’s available for all major platforms (Mac, Windows, Linux, iOS, Android), including on F-Droid.
I did not say people who use it. I said people who advocate for and regularly use OSS. Plenty of people use open source software because it is the most popular or it is what was recommended to them. Obviously that group exists in large number.