Running Outlook on the iMac causes the screen to flicker and eventually black out and reduce to half/split screen display.

I also have a 2015 27" iMAC and am having this same issue with Outlook 365.

I believe it to be a video driver issue and of course, you can't download or update MAC AMD video drivers.  I think some video call is being made by Outlook that the driver doesn't like.

As far as I can tell only machines with the M9 series (possibly specifically the 390) series is affected.

Does anyone have a different video card than that?

I have tried light mode in both Outlook and macOS but that did not help me.

I have tried reinstalling O365 and that did not help me.

Apple recommended an OS wipe and reload but that is not going to solve this, they just don't know where to go next.

I have contacted AMD with the relevant details and I will post any replies I get.  There are rarely video driver updates from Apple/AMD where people are used to almost monthly releases from NVidia with new features and fixes.

The only think I would say with this is that I never had a problem before upgrading to Mojave. When I previous OS versions like Sierra and El Captain I never had the issues. So Apple Can say it's Microsoft but maybe it's the Apple OS. I've deleted and reinstalled the latest version of Outlook on the 18/06/2019 and it does the same thing!

Aplle has got nothing to do with this. I've had this issue way back before Mojave and dark mode was released. Actually i was hoping Mojawe would fix this issue, but it did not.

Meanwhile i fixed the issue by buying an iMac 2019. Thanks Microsoft....

The pre-Mojave version works a treat.   I switched back to this when the problem first arose,  but after about 3 months I upgraded again , but had lost my timemachine backup, so could not restore to the previous version.   It is great to get the link to the previous version, so thank you. 

Another workaround if you do not want to rewind your version,  is to change the resolution on your Mac.   It only seems to occur on the default resolution, either scale up or down.  It is definitely a Microsoft problem and related to the screen solution

I have  tried changing my screen resolution the flickering still occurs, it can take anywhere from a few minutes to a week or so to appear but unfortunately leaves outlook unusable, unless I run windows under Parallels.

The pre-Mojave version works a treat.   I switched back to this when the problem first arose,  but after about 3 months I upgraded again , but had lost my timemachine backup, so could not restore to the previous version.   It is great to get the link to the previous version, so thank you. 

Another workaround if you do not want to rewind your version,  is to change the resolution on your Mac.   It only seems to occur on the default resolution, either scale up or down.  It is definitely a Microsoft problem and related to the screen solution

Seems to me we need to get the version of outlook that was runing BEFORE the Mojave upgrade and install that. Lets start from there. What was the Outlook Version back then?

Believe pre-Mojave would be more more less 16.15 , July 2018 or 16.16 August 2018- try and let us know .

Link.....

https://docs.microsoft.com/en-us/officeupdates/release-notes-office-for-mac#september-2018-release