Using older versions of Outlook for Mac for personal email and calendar
I had exactly the same issue. After reading the various replies, I checked out the Outlook issue mentioned. My Outlook automatically launches, but I quit the application prior to launching anything else (Photoshop) and, hey presto - no flickering, no blackouts. I hope that the issue is now resolved for good. I intend uninstalling my office 365 applications which won't be that convenient, but as I was on the verge of buying a new imac, it is a small sacrifice. Many thanks to those who suggested that Outlook might be causing the problem.