iMac 27 inch 2020 - Screen Glitch (Random Lines Appear on Screen)

Try the following: download and apply the macOS Catalina 10.15.7 Combo Update   

It fixes this issue:

• Addresses a graphic issue that may occur on iMac (Retina 5K, 27-inch, 2020) with Radeon Pro 5700 XT

I was having the exact same issue with my 2020 iMac 27".. I had order the Fully loaded iMac But i did only 4TB SSD and 5700 XT 16 gpu and even during a clean install/setup it was doing it during that too. When i tried to take a screen recording via the computer itself it came back with clean video, but recording from an iPhone on slow motion recording i caught it..

I sent mine back and a new one is on the way, hoping the new one doesn't have the same issue. that would suck...

But i am so glad to see i am not the only one with that issue, but not sure if this makes me feel better or not now lol

Tom

Have had my iMac 2020 with i9, 5700XT for about a week now and the white line glitch was annoying the life out of me. Sometimes blinking on the left side, other times on the right. Sometimes it would occur every five minutes, other times only once in an hour or two.

There are a couple of known workarounds so far, based on comments across the internet, from users affected by this glitch:

1. Connect a second screen

Apparently connecting a second screen somehow completely eliminates the glitch. I personally don't want to attach a second screen and trying to use a headless HDMI plug didn't go well (causing bluetooth lag). So that's a no go for me.

2. Change the screen resolution

Users reporting that the glitch is gone with any resolution other than the default 2560x1440. So yesterday I created a custom resolution 2528x1422 in SwitchResX, switched to that, and I have not seen the white line glitch since then. Has been just over 24 hours now, glitch free 🤞

So, yes, the new update to MacOS 10.15.7 has completely got rid of the white line issue... so, yes, it was a software fault as everyone expected.

But, does anyone find they're missing their white lines now they're gone? My Mac used to be special, and now it's just the same as all the rest.

Take a screen shot & view that in Preview, move the Preview window around, if you see double lines it's a Video card/VRAM problem, if the lines do not move moving the pic around then it's the LCD or cable.

There is a big discussion on this glitch problem at the macrumors imac forum. Search for the discussion thread, "iMac 2020, 5700XT - graphical glitch?" Right now, that thread is pinned to the top of the MacRumors iMac forum.

They have poll where, so far, 24 people out of 37 users of the 5700XT model, i.e. 65% of people are experiencing this problem. Note that this problem, according to the poll, only affects users who have the 5700 XT graphics card. The link to that thread is here:

https://forums.macrumors.com/threads/imac-2020-5700xt-graphical-glitch.2251034/

For those trying to reproduce the issue, in my case it behaves like this:

• regular occurrence every 30-40 minutes, without any special events executed
• if I watch YouTube in Safari it can occur more often
• if I watch QuickTime video it can occur more often
• if I’m on a (Slack) video call it can occur every 5 minutes

None of these are reproducible reliably though. Not sure what’s the exact trigger.

For those trying to get rid of the issue and wait until an official fix is out, on MacRumours it’s been confirmed that it doesn’t occur when:

• you change your screen resolution to something else from default (SwitchResX has good options)
• or when you connect a second display

Issue was fixed two updates before. Just update your macOS ;)

Hi, I have experienced it the moment I finished the initial setups. I asked Apple Support and they told me to reset the SMC and NVRAM to solve the problem. It actually did for me, but I haven't started editing videos just yet, so it might not be stressful enough for the system to glitch again.

@Bunn_pt, I just got off the phone with Apple CS. They were transferring me around and I had to explain my situation 4x all over again, just to be told I have to arrange a return. Have to send it back for a replacement. Not sure what good is it for, if there's no guarantee the replacement wouldn't have the same problem.

Just return it ASAP. That’s what I did.

I downgraded to Catalina, so far, no more issues. I dont think Apple will take back the PC because of software. The B.S. operating system is buggy as heck

Same problem with my iMac 2020, already appeared during the initial Mac setup and keeps flashing randomly since then. Searching through YouTube and google it seems this is a common problem with the 5700XT gpu that comes with it.

I’m thoroughly disappointed, waiting for the customer service chat to come back online.

There are users who say that it does not appear when you use 2048x1152 screen res. Temporary solution.