Please help with this issue - iMac 24 M1 display issue

You're experiencing 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 ⅔'s of a new Mac Mini M4.  

You have these 4 options to consider:

#1 - pay the ~$600 US price for  Apple or an Apple Authorized Service Provider to repair the monitor (which is over ½ of a new M4 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 iMac.  If considering this option consider the following: a 10 Core Mac Mini M4 with 16 GB RAM and 1 TB SSD ($1084 US) with a 32" LG 4k monitor ($331 US) from Amazon.com)  is $1415 which is $541 less than a similarly configured new 24" iMac ($1956 US)  re 07/2025. 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.

looks like a hardware defect

if it was me then I would

try restarting the computer if it did not

then I would try Erase your Mac and reset it to factory settings - Apple Support

if that did not resolve it then I would contact apple about repair Contact - Official Apple Support