Display problems with the new iMac that's not even 2 years old

I bought the new iMac (2021) in the year it was released in August, so it's not even 2 years old. All of a sudden, when I was using the device, black horizontal lines appeared on the screen and the top left corner of the iMac was heating up. I'm surprised as to how a product that's not even 2 years old could have such major problems.

Took it to the service providers at iCare who said that the device passed all the Apple diagnostic tests. They suspect it's a problem with the display but cannot confirm unless the open it up to replace it which is going to cost me a third of what I originally paid for it. Customer support has been pretty unhelpful too and refuse to connect me with someone who might be able to escalate the complaint. Any idea on what I could do to take up the matter further? I'm really at a loss of what to do since replacing the display would be too expensive, especially when nobody can even confirm what's wrong with it in the first place.