My 24-inch M1 iMac's display

If your warranty expired and you selected to NOT buy AppleCare then the repair would be at your expense. AFAIK Apple does not have a repair program for M1 based 25" iMac displays. The last cost I heard of was in the $600 range, as we have no idea where you are located your should contact your local Apple Store or Apple Authorized Service Provider to find out more detailed information.

Also, you may already know this but these forums are for end users (I am an end user just like you) Apple is our host however they do not read or participate in the user to user forums. If you want to speak directly to Apple, please call AppleCare. Just click the following link and you input your country and the phone number for that area will appear: AppleCare Contact Info.

Best of luck.

Hi,

I doubt Apple repair your iMac display for free.

Try to connect external monitor and see if it's also showing horizontal lines.

In case you have not seen it, there is an on going thread that you should visit.

@ > Persistent horizontal lines appear on iMa… - Apple Community

You're not alone: Persistent horizontal lines appear on iMac screen. Several users have reported the cost of the repair to be around $600 US.

If you consider getting it fixed or getting a new iMac as a replacement consider the following: a 10 Core Mac Mini M4 with 16 GB RAM and 1 TB SSD ($1084) with a 32" LG 4k monitor ($331) from Amazon.com)  is $1415 which is $541 less than a similarly configured new 24" iMac ($1956)  re 07/2025. Keep your keyboard and mouse from your current Mac for use with the Mini. The prices preceding are before tariffs.

I got the above Mini with a 32" LG 4K monitor w/speakers for only $60 more than the 27" (didn't know the Mini had a speaker).  There are many monitors available in 27" size on up for $100 to $500 depending on what features you want. 

Just some food for thought.