Why Horizontal Lines on iMac 24" (2021): A Widespread Hardware Issue?

If you’re seeing persistent horizontal lines on your iMac 24″ screen — especially across the lower two-thirds — you’re not alone. Many users who purchased the 2021 M1 iMac have reported similar issues, especially after auto-updating to recent macOS versions like Sonoma 14.6.1. While it may seem like a software glitch at first, evidence suggests this may be a common hardware defect.

Symptoms and User Experience

Affected users commonly describe:

Flickering or shimmering horizontal lines
Lines that degrade font and display quality
Strain on eyes during regular usage
The issue appearing suddenly, sometimes after an update
A fully functioning iMac otherwise — only the screen is affected

For professionals and everyday users alike, this issue disrupts productivity and usability.

What’s Likely reason for Horizontal Lines on iMac 24?

Community discussions and some expert insights suggest this is not merely a software glitch:

The Flat Flexible Cable (FFC/FPC) that powers the LCD is believed to be the root of the problem.
This cable handles high voltage (up to 50V) and may degrade over time due to heat and stress.
As it deteriorates, signal interference and short-circuiting can cause the flickering lines.
If left unresolved, this can lead to permanent screen damage.

No Easy Fix

Unfortunately, this is not something you can fix with a settings tweak. Users who visited the Genius Bar were often quoted expensive repair costs — despite the issue appearing to be a design flaw.

Some temporary steps you can try:

Restart the iMac in Safe Mode to see if it changes (unlikely, but worth testing).
Connect an external display to verify that the GPU is not at fault.
Submit feedback via Apple’s feedback page — the more reports, the more likely Apple will respond.

What Can Be Done to fix Horizontal Lines on iMac 24?

Out-of-Warranty Repairs: Unfortunately, most affected devices are now out of warranty. Still, some users have been successful in escalating their cases through Apple Support, especially when citing the widespread nature of the issue.
Public Pressure: A recall or extended repair program could happen if Apple recognizes a pattern. Keep posting in forums and submitting feedback.
Consumer Protection: Depending on your country, consumer protection laws may help. In the EU and some parts of Asia, devices must last a “reasonable” lifespan, and this may qualify for free repair or replacement.

Final Thoughts

It’s extremely frustrating to face hardware failure on a premium device just a couple of years after purchase. The iMac M1 was praised for its sleek design and powerful performance — yet this screen issue casts a shadow on its reputation.

If you’re facing this problem, you’re not alone. Speak up, file reports, and share your experience online. With enough visibility, Apple may be compelled to take responsibility and offer a fix.