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.
If you prefer not to self-host Jitsi and be identifiable via your domain, there’s jami.net as a replacement for Jitsi. It is a decentralized conference app that requires you to install an app. However, it’s open-source and account creation is optional. It’s available for all major platforms (Mac, Windows, Linux, iOS, Android), including on F-Droid.
Tell them that it works the same way, no registration too, but the old one had to shut down.
Technically, it did shut down, for those that don’t want to log in with anything.