4K Display on 2013 Mac Pro has Strange Flickering Lines

Those single-pixel-high streaks are typical of display-memory under-runs, where the display memory did not respond in time and the data had to be blanked for one screen refresh period. [It is possible that the use of poor-quality cables on a very high resolution display could cause them. ¿Are your cables rated for "5K" ??]

In the old days, those would have been dark streaks that lasted only one refresh period. With Dark Mode it is harder to diagnose, because they are sometimes reversed into light streaks (harder to ignore).

Apple's standard is to have no such under-runs, ever. Your display output should at all times be cinema quality, no defects.

To eliminate the cable as the source of the problem, you could use a high-quality cable such as this one:

Monoprice Select Series Mini DisplayPort 1.2 to DisplayPort 1.2 Cable, 6ft Product # 13373 $5.80

Otherwise the under-run occurs in the display card (inside the computer), not in the display.

I have the same artifacts with MacPro 2013 and Sony 4k TV but only when RME TotalMix FX window is open.

And only when the window is in 100% view (sometimes).

My connection has a special adapter to support 60Hz 4k HDMI.

I will live with that, until my ordered Mini M1 will arrive ;-)

The issue at the Genius Bar will be duplicating the issue.

If you depend on them to find the issue,they will run the diagnostic, find nothing wrong, and send you away with no fix.

Once you and the genius agree it is happening, you are almost done.