Unfortunately, that's the case: Safari and Firefox haven't yet implemented WebRTC Insertable Streams, which we use for end-to-end encryption. And on iOS even Chrome is not really based on chromium (due to Apple's restrictions). We know support for the latest WebRTC standards is on the roadmap for Firefox (not sure about Safari).
So for the time being we support chromium based browsers (Chrome, Vivaldi, Brave, Edge, etc.).