It seems as though Microsoft has change their authentication methods. Does Zulu support the new methods? 

I am on v4.0 and do not see anyway to change auth method. The changelogs don't mention anything, and haven't been updated since July 2021, so I assume not.

 

Update for others:

I have heard back from 360works and this is indeed due to Microsoft's authentication changes. They are working on an update for Zulu and plan to have it out before final EOL on the basic authentication. Upgrade instructions: https://techcommunity.microsoft.com/t5/exchange-team-blog/basic-authentication-deprecation-in-exchange-online-september/ba-p/3609437

I can confirm re-enabling basic auth fixes the zulu issues.