Screen flickering - 2021 M1 iMac 24

It appears that you might be a victim of the M1 Mac defective display issue:

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

Persistent horizontal lines and other issues on iMac M1 display

Several users have been told by Apple that the repairs would cost around $600 US. My recommendation to you is to take it into the nearest   Apple Genius Bar for a free diagnostic exam and estimate of repairs. If you're still under Apple Care they'll fix it for you free. If not it'll be your responsibility. But at least you'll be in their system if ever Apply does a recall fix.

If you're on your own for the repair several others were considering getting a 3rd party 27" 4K monitor to run off the iMac. I got a 32" LG 4K monitor for $327, about half of Apples cost to fix it. (I didn't have a M1 iMac but got the monitor to pair with my new Mac Mini M4)

It's likely a hardware issue then, if you did not purchase AppleCare then any repairs would be your responsibility assuming my hardware hunch is correct. The only suggestion I can offer is to try restarting in Safe Mode which I don't think will fix your issue but it's surely worth a try.

Apple does not have any repair programs open for 2021 iMacs at this time. We understand your frustration and suggest that you submit feedback to Apple at www.apple.com/feedback.

These forums are not a venue to vent, as you likely know we are simply end users just like you. Apple is the forum's host however they do not read or participate in the user to user forums.

As to whether it is product related problem I doubt it. We have seen well over 100 users with 2021 24" iMacs have similar issues. Apple recommends AppleCare (I always buy it) to cover any repairs after the 1 year warranty expires however there are many people that ignore getting it, sometimes they don't have any problems and sometimes they do, it's a gamble. On this gamble you lost.

Apple has a history of putting repair programs into place if they see a widespread issue, my guess is even though we have some many users complain (over 100 or so) apparently the issues is not widespread enough to warrant a repair program so for users like yourself that lost the AppleCare gamble you have a decision to make, repair or replace. I don't have an opinion on paying the repair cost, to me $700 is a considerable expense. Of course if you pay the $700 and Apple implements a repair program you would be eligible for a refund, again another gamble though. So of course the decision is yours.

If you decide to cut bait and move on from the 2021 then I'd consider a new (or Apple refurbished) 2024 M4 Mac mini. One with 16GB of RAM and a 1 TB SSD will cost you $999 (that's new) and a display (27" 4K display) starts at about $300 and you will have a new machine (get AppleCare this time) that is faster and more capable than your 24" iMac with 8GB of RAM. If I was in your shoes, that may be the road I'd take.

Another option is rather than replacing your current iMac's display for $700, get an external display and connect that to the iMac and make it your primary display. For $300 you have a solution, one you can use in the future too with your next computer purchase.