MacBook Air M2 - Display showing LCD BIST (solid colors) after wake.

External monitor works fine.

That strongly suggests a hardware failure. You've done one appropriate home check already. Here's another that might narrow down the suspects for a service provider:

While the display is showing anything (good of bad) on-screen, GENTLY move the display assembly through about 60° of it range of motion while looking at the image.

If the image flickers and changes as you move the display and stop when you do, the most likely source of the fault is a worn/damaged display cable.

Still, this is not goingot be an at-home fix, and will be expensive. The display—including its cable—is one sealed assembly and parts cannot be separately replaced. One failed part means a new display assembly.

As other end user from all around the world, we cannot make repair estimates on Apple's behalf. However, based on similar user posts here, it appears parts + labor cost for a laptop display assembly replacement through Apple or an Apple Authorized Service Provider start aounds US$500 and goes up with screen size.

josueonfroyy wrote:

My main problem now is that I bought this MacBook as 'Brand New' less than a year ago (March 2025), but when I check the Serial Number on Apple's website, it says the coverage has already expired. This suggests the seller might have deceived me. Since I don't have the original invoice yet (the seller is refusing to provide it), is there any way to get Apple to fix this for free based on the purchase date, or am I stuck with this expensive repair because of the expired status in their system?

FYI, If the seller was not an Apple authorized reseller, then you bought a secondhand laptop even if it had never been opened or used by the seller. The warranty clock starts when the laptop is first sold and an unauthorized reseller would be the first "owner" even if the box was never opened.

This can also cause you problems if your laptop ever becomes locked out for any reason. Without being the first/original owner of the device in Apple's eyes, then you won't have the necessary proof of ownership which will be acceptable to Apple to let them unlock the device for you.

Only an Apple authorized reseller can be a middle man between you & Apple as far as initial ownership goes.

Sorry for the bad news.