iMac display shows horizontal lines and flickering in bottom section

If you have a M1 iMac you're probablyexperiencing what many other M1 iMac owners are experiencing: the following topics illustrate the Silicon M1 iMac Display problem:

Screen Failure on 24-inch-iMac, M1, 2021 - Apple Community

Persistent horizontal lines appear on iMac Screen - Apple Community

Horizontal Lines on Screen of iMac, 24", 2021

Horizontal black lines covering bottom 3rd of 2021 M1 iMac screen

Grey horizontal patches on my M1 iMac 2021 model

Horizontal lines at the bottom of iMac(M1,2021) screen

Horizontal Lines on 2001 M1 iMac Display

M1 iMac Display vertex heating to scorching 55°C  — Seeking Advice on Escalation

Horizontal Lines on iMAC with M1 chip

Others have reported that the repairs will cost about $600 US.  That's about ½ of a new Mac Mini M4.  

Amoung the options you have are these 4 to consider:

#1 - pay the ~$600 US price for  Apple or an Apple Authorized Service Provider to repair the monitor (which is about ½ of a new M6 Mac Mini).

#2 - get a monitor and use it with your M1 iMac.  You can get a 27" or 32" monitor from $140 US on up. 

#3 - get a new Mac.  If considering this option consider the following: a 12‑core CPU, 12‑core GPU Dual 16‑core Neural Engine Mac Mini M6 with 16 GB RAM and 1 TB SSD ($1399 US) with a 32" LG 4k monitor ($331 US) from Amazon.com)  is $1716 which is $450 less than a similarly configured new 24" M4 iMac ($2199 US). Keep your keyboard and mouse from your current Mac for use with the Mini. 

#4 - keep tabs on the Apple Service (Recall) Programs - Apple Support in hopes that a recall/repair program is activated.

Just some food for thought.

There is a well-documented pattern of display problems affecting some 24-inch M1 iMacs (2021). 

Reports describe symptoms remarkably similar to yours: horizontal lines concentrated in the lower portion of the display, flickering, grey bands, and even “ghost” or duplicated images from other parts of the screen appearing in the affected area. 

Apple Community and MacRumors reports have documented this pattern across multiple users. (Apple Discussions)

One particularly relevant Apple Community report describes “overlapping lines at the bottom of the screen” on an M1 iMac. 

The user reported that reinstalling macOS made no difference and that the lines did not appear in screenshots. (Apple Discussions) 

Another report describes horizontal lines and flickering near the bottom, with the problem persisting after restarting. (Apple Discussions)

The timing also fits the reports. 

Many affected owners have said the problem appeared roughly 18–24 months after purchase, although other reports describe failures after around three years. (MacRumors)

There is, however, an important distinction: Apple has not publicly confirmed that there is a specific underlying design defect causing all of these cases, and as of the sources 

I checked, there is no Apple service program specifically covering this M1 iMac display problem. 

Apple Community participants were still reporting the absence of such a program in 2025–2026. (Apple Discussions)

So I would characterize your situation this way:

Your symptoms are highly consistent with the recurring M1 iMac display problem reported by other owners. That makes a normal macOS/software problem substantially less plausible. The fact that content from the functioning portion of the screen appears duplicated/reflected in the damaged lower section is particularly consistent with the reports I found. (MacRumors Forums)

I would therefore not recommend reinstalling macOS or spending much time changing software settings. You can still perform Apple Diagnostics if you want an official diagnostic record, but I would also photograph/video the problem and have Apple or an Apple Authorized Service Provider examine the iMac.

Have the computer evaluated by the Professionals who have the Special Hardware Software and Expertise to diagnose the issue and offer possible solutions

Make an Appointment at the Apple Genius Bar or call 1 800 MyApple and have them evaluate the computer

Other location Call Centres 

 Contact Apple for support and service

The horizontal lines and flickering on your December 2023 iMac with an M3 chip, particularly the way the bars appear to reflect content from elsewhere on the display and distort during video playback, suggest a possible display hardware problem, although the exact cause cannot be determined from the symptoms alone.

Since restarting and allowing the iMac to cool have not resolved the issue, I recommend having Apple inspect the display rather than continuing to troubleshoot macOS. Before your appointment, back up your important files and record the distortion if it reappears. You can also run Apple Diagnostics , although a normal result would not necessarily rule out an intermittent display fault.

Tten I would agree with @ Old Toad and arrange an inspection at an Apple Store or Apple Authorized Service Provider, and show them your video. Ask for a diagnosis and repair estimate before authorizing any paid repair.

As your iMac is approaching three years old, check whether any AppleCare coverage or applicable consumer-law protection remains. Apple's Mac service and repair information  explains the available service options.

The main point: The symptoms warrant a hardware inspection, but it is too early to conclude that the entire display needs replacement. Apple will need to determine whether the fault lies in the display panel, its associated electronics or another component.

Have the computer evaluated by the Professionals who have the Special Hardware Software and Expertise to diagnose the issue and offer possible solutions

Make an Appointment at the Apple Genius Bar or call 1 800 MyApple and have them evaluate the computer

Other location Call Centres 

 Contact Apple for support and service

you can read about it here

iMac 24inch M1 Screen Defect - Apple Community

Hello Owl, thank you for your response. I should inform you this is not an Apple M1 series computer it has a M3 chip in it but I don't think that is much important to this discussion right now...

To add some more of the information to this thing: at times I would see the number of bars increased by one or two they would stay for a second or two and then and then they disappear. They will do this habit for time to time..

Another thing that has started to happen is that whenever I'm playing some kind of video on the display, bars would try to reflect whatever is going on in the video and they would start to glitch out and spasm. It would start to shake really badly, it just looks really weird.

I haven't been able to take a video of this happening since I am unable to replicate the issue at the time of writing, if it does happen again I will post a link for the video in the replies.

thank you for all of the information you've given, I've given it all a read. I will visit the Apple Store in a few days and I'll see where it goes from there. Thank you so much.

Hi, thank you very response OldToad. I should have clarified in the original proof that this is a M3 iMac not M1. Totally my fault, thank you for your suggestions. I've scheduled an appointment with the genius bar at my local Apple store. I'm going to get this computer checked out.

I just wanted to add onto another response of mine (continuation of my response to Owl-53, another person who has contributed to this thread): I mentioned the horizontal bars start to glitch and spasm out for some reason and it's really weird. I wasn't able to get a video of it at that time, but I've been able to capture the issue now, I'll just share the link to the YouTube video documenting this issue so everyone can have a look at it.

initially the glitching looks something like this:

https://www.youtube.com/watch?v=AP4C6ogV8D8

and then it ramps up to this level of glitchiness (it takes around half an hour or something to do so.)

https://www.youtube.com/watch?v=XHpc4203Kk0

Okay, I had the computer checked out by the genius bar today.

Initially they asked to keep the computer for 48 hours to rule out a software issue of any sort, after starting the computer up and inspecting the screen the employee said "no, it's not a software issue. your display has some issues and it'll need to be replaced"

the employee cited the costs for replacing the screen to be ~60,000 INR i.e 885 CAD (tax included).

i think i'll just leave the screen be and invest in a newer computer later down the line as the flickering is in the bottom of the screen and doesn't affect my usage much (i hope it wont get much worse than it already is...)

its quite sad to see that these issues have not been acknowledged and or no proper recall has been issued yet.. :(

thank you so much for your help.

Thank you for the update. I am glad you were able to have the iMac examined at the Genius Bar and get a clearer understanding of what is causing the flickering.

I can certainly understand why you would decide to leave the display as it is for now, particularly if the flickering is limited to the bottom of the screen and is not interfering significantly with your day-to-day use.

Given the cost of a display replacement, waiting and considering a newer Mac when the time comes seems like a perfectly reasonable approach.

I am sorry that this has been such a disappointing experience, though, especially when you have otherwise been happy with the computer.

Hopefully the flickering remains limited and does not interfere with your use of the iMac.

Thank you for letting us know what the Genius Bar found, and I am glad we could be of some help along the way.

I hope you will be able to continue getting plenty of good use out of the iMac for the time being.

Thank you for the clarification

Will look in this matter further, taking into account the is a M3 iMac

Hi, thank you very response. I should have clarified in the original proof that this is a M3 iMac not M1. Totally my fault, thank you for your suggestions. I've scheduled an appointment with the genius bar at my local Apple store. I'm going to get this computer checked out.

I just wanted to mention in another response of mine to Owl, another person who has contributed to this thread: I mentioned my display the bar start to spasm out for some reason and it's really weird. I wasn't able to get a video of it at that time, but I've been able to capture now, I'll just share the link to the YouTube video documenting this issue so everyone can have a look at tthis new issue..

initially the glitching looks something like this:

https://www.youtube.com/watch?v=AP4C6ogV8D8

and then it ramps up to this level of glitchiness (it takes around half an hour or something to do so.)

https://www.youtube.com/watch?v=XHpc4203Kk0