I am a producer for a company-wide Live Event. When I click the link sent in email, I get a warning that I need to switch back to classic teams, but it doesn't work. I also no longer have a toggle in the upper left corner of Teams to switch back. It's as though I'm now trapped in New Teams and I'm not finding any help for my scenario.
I was able to fix it after reading this post, which suggested opening Teams web and then choosing to download the desktop version of Teams. After installing that (did not have to uninstall Teams first), I then had Classic Teams as an app. I was able to run that and then join the Live Event as a producer... 30 minutes late. What an awful experience!