While Jitsi is open-source, most people use the platform they provide, meet.jit.si [http://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 [http://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.
If you rely on a single service this much you should either pay for it or selfhost.
Edit: What I wrote might sound aggressive but I don’t mean it in a bad way. I understand your concern, just wanted to point out that one should be ready for free (or any for that matter) services completely changing direction, conditions, or getting decommissioned.