Thanks for the feedback! We are working on this.
Current Dark Mode support: https://docs.microsoft.com/en-us/officeupdates/release-notes-office-for-macAnonymous commented
Dark mode is now broken. The message body display uses a dark background even when all the elements inside are rich and designed for a light background. The HUGE button on the ribbon to "Switch Background" only works for a single message?? It should be a toggle, and much smaller.