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

OK - I asked the question, kept searching and have found the answer.  I have a 27 inch iMac circa late 2016.  Issue is with Outlook and Apple os compatibility.  Checking the low resolution box in Outlook solved the problem.  Apple and Microsoft have finally admitted the problem and they are supposedly fixing the compatibility issue with the os update due in late september (catalina).  So for those who think (and advised) that you should ditch your iMac, lose all your data and the like, I am so happy I did not take your advice.  Thanks to everyone who commented

Reason I bought a 5k iMac is for the fantastic resolution ......Low resolution for me is not the fix -

I think you are misunderstanding what low resolution mode is.  It only affects the single application being used (Outlook), one of your other applications or desktop is affected.  You don't loose any resolution at all.

-Quit the application

-Go to the Applications folder.  

-Select the application you need to run in low resolution mode.  In this case, Outlook.

-Go to "Get Info" You can do this any of three ways (1) Right click and go to "Get Info" (2) Left click the application, click on file, click on "Get Info" (3) Left click the application, press command and "i" on the keyboard

-Toward the top of the window that opens, check the box next to "Low Resolution Mode"

This is a workaround, not a fix, true.  But emails and calendars aren't exactly something I'm clamoring to see on a Retina display.

It's now been a week since I enabled low resolution mode for Outlook and the issue has not returned.

This worked for me.  And yes you can’t choose a specific  resolution just more space.  On other Macs you can be specific. 

I came across this article.   Another workaround might be to set up Outlook to run in Low Res mode.  See article below:  I will try this and see how this goes.. 

https://support.apple.com/en-gb/HT202471

Using apps with a Retina display

If an app looks different than you expect on your Retina display or high-resolution external display, try opening the app in low-resolution mode:

1. Quit the app.
2. Open the Applications folder.
3. Click the app once to select it, then choose Get Info from the File menu.
4. From the Get Info window that opens, select the checkbox labeled ”Open in Low Resolution.”
5. Close the Get Info window and open the app again.

Some apps that work best in low-resolution mode or that work only in low-resolution mode will have this mode already turned on, and in that case you might not be able to turn it off. The app developer might offer an update that includes support for the Retina display.

I have exactly the same issue. Already tried restart, reset SMC, even did a clean install of OSX. But everytime i open Outlook and start scrolling  through the mais, the screen flickering appears. If i don't use Outlook, the system runs fine. On my system it's not related to Skype. It's just scrolling through the mails, that causes it. I also have the iMac late 2015

Hi Luke,

Since regular Skype is a completely different product from Skype for Business, if you have the similar issue when running regular Skype, we recommend you post a new thread under Skype category. The relevant team will provide the dedicated suggestions for you. Your time and understanding will be highly appreciated.

Regards,

Marvin

Hi Marvin,

Whilst I appreciated the response, I do seem to be getting the run-around by you guys. I'm being told to post in Outlook forums, in Skype forums etc. It's not down to me to find where the issue is and then post in the correct place, it's up to you to support a paying customer and advise me where the issue is and how to resolve it.

I'm not the only person experiencing this issue and from what I can see it's not been resolved.

There is clearly an issue with Microsoft Office and macOS Mojave. The issue did start after an Office 365 update and not after an macOS Mojave update so that points towards Office 365 being the issue.

Can't someone look into this rather than giving me the round-around and telling me post else-where.

Many thanks, Luke.