2017 27" Mac Graphic card issues?

I’d schedule store bring-in hardware repair. They’ll estimate it for free but expect it to be at least $300-$500 for board swap. Decline & shop for new. Good luck!

FYI: after 2011, iMacs do not have video "cards." The video hardware is integral with and soldered to the logic board; bad video hardware means a new logic board.

Hi Iron Paw,

The graphics issue you're experiencing is, unfortunately, a hardware issue either with the display or graphics card. Regardless, I recommend you contact Apple Support for service options: Get Support.

Cheers,

Jack

In rkaufmann87's very pertinent 2:07PM Jun 3 reply:

If it drives external displays with no problem then the GPU is fine.

...lies the one home diagnostic that can help you budget. Can you beg or borrow an external for testing?

The display for a 27-inch thin-line iMac like yours is rather pricey because it is a sealed assembly with cable, display and cover glass in a single package unit, However, it should be cheaper than a logic board.

Have you run diagnostics? Use Apple Diagnostics to test your Mac - Apple Support

It may confirm your suspicions.

If it drives external displays with no problem then the GPU is fine.

id recommended that you post an EtreCheck report of your system and we can search for issues.

I have to ask, has this iMac been opened for service or a DIY upgrade?

If so, then perhaps the display cable and board connections are either loose or damaged.

This sometimes happens running older OS background and Screen Savers. Try changing those and the Dynamic Desktop to see if you can see a difference.

Guessing if it is the GPU, Cabling or Display is not a good idea.

I concur with Jack-19, that you should have the problem diognosed by an Apple Store or competent AASP.

I doubt that this will make any difference but have you tried changing the display scaling?

There is one major issue that I see.

The best antivirus, cleaning app, and overall maintenance app for Mac OS is Mac OS itself. All you need to do with Mac OS to keep it secure and running well is to keep it up-to-date and do periodic (about 1x per week) restarts. Other than that, leave it alone. Adding third party antivirus, cleaning, security and other types of maintenance apps to Mac OS adds no additional level of security. The only thing these apps do is have the opposite affect users want. They make Mac OS slow, unstable, generate odd behavior (much like you are experiencing) and make Mac OS appear buggy. 

Please locate the developers uninstall instructions for Open VPN and follow to the letter. Then restart in Safe Mode per the directions in Use safe mode to isolate issues with your Mac and then restart normally. 

No your VPN app is not AV however is equally worthless and equally damaging and should removed.

removing it may not fix your problem however keeping it does nothing to make your system more stable, hence my urging to have it removed.