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

24 hours in and low resolution mode fixed it for me.

Late 2015 iMac and Radeon R9 M395

I am confirming what a lot of you already said in this post: The issue is Microsoft Outlook.  This program causes the flickering, excessive flashes/black screen issues in Mojave 10.14.5.  I did not have this issue pre-Mojave though.  In High Sierra, everything worked fine (maybe my Outlook was also an earlier version so maybe thats why it was stable?)

I went through every diagnostic - hardware and software, spent days backing up, erasing hard drives, restoring application one at a time, etc. And once Outlook gets launched - flickering screen.  Its maddening!  The issue has been known now for over a year and nothing has been done about it?!

I now resort to Mail or use Outlook via webmail.  Shouldn't we get a refund for a product that we PAID for that doesn't work on our Mac/OS as stipulated?

Someone please post a patch of some sort if Microsoft cant seem to get around to it.

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 changed the resolution of my built-in retina screen from Default to "More Space" (you can't actually choose a resolution as far as I can tell) and it seems to be stable now.

System Preferences - Displays - Display tab and Scaled radio button

I have been running in this configuration for a couple of hours now with Outlook open and it's been fine so far.

I'm going to run this way as my default.  I'll report back if the problem comes back or in a few days with a status update.

Looks like you are right.   Details of my graphic card below:

AMD Radeon R9 M395:

  Chipset Model: AMD Radeon R9 M395

  Type: GPU

  Bus: PCIe

  PCIe Lane Width: x16

  VRAM (Total): 2 GB

  Vendor: AMD (0x1002)

  Device ID: 0x6920

  Revision ID: 0x0001

  ROM Revision: 113-C905AA-799

  VBIOS Version: 113-C905A1-007

  EFI Driver Version: 01.00.799

  Metal: Supported, feature set macOS GPUFamily2 v1

  Displays:

iMac:

  Display Type: Built-In Retina LCD

  Resolution: 5120x2880 Retina

  Framebuffer Depth: 30-Bit Colour (ARGB2101010)

  Main Display: Yes

  Mirror: Off

  Online: Yes

  Rotation: Supported

  Automatically Adjust Brightness: No