GoToMeeting claims end to end encryption[1] and in the same sentence say it's just SSL just like Zoom. Never the less they offer call-in as well so end to end becomes impossible right there. I have serious doubts about any conference software offering real end to end encryption as it's unrealistic for clients to be dealing with that many av streams.
1. https://support.goto.com/meeting/help/security-faqs-g2m05001...