This issue has been resolved. If you haven't already, please download the most recent version of Zwift.
Posted May 23, 2021 - 16:21 UTC
We are still working to find a solution and at this time are encouraging users on Mac machines to update their operating system to Big Sur if they are willing and able, as this has proven to be a viable workaround.
Posted May 20, 2021 - 22:29 UTC
We are aware of an issue affecting some users on Mac and PC where, after updating to the newest version of the game, they are unable to login. We are currently investigating this issue. This issue only affects the launcher.