I have the same problem. Yesterday, I came back to my desk after lunch and the Macbook Air that I purchased in January of 2021 had thin horizontal lines across the entire screen top to bottom. I turned my computer off and restarted a couple of times because that is always the first advice one is given with computers. That didn't work so I immediately called Apple. I was on the phone with them for 37 minutes and the person I spoke with had me hold Control, Option and Shift for 7 seconds and then press the power button and hold all 4 keys for 7 seconds. Afterward, I found the support page where the information is clearly laid out: https://support.apple.com/en-us/HT201295
However, despite attempt after attempt, the screen only got worse and I got vertical lines in addition to horizontal lines. He had me keep going. Then the screen started to flicker. He had me try the reset again and then my screen went completely black while we were on the phone. He set me up to go to a store in the area to have it checked out and I have the appointment today. The screen is no longer black but I have the thin horizontal lines and it continues to flicker periodically (I don't know how else to describe this). When I reboot, I have the horizontal lines, vertical lines and the flickering.
The computer has not been dropped and has no damage. I spent a lot of money on this new computer -- I even upgraded to the 512 GB of storage. This should not be happening and I will update on the progress of this issue since I see that I'm not alone in having this problem. If anyone else had this problem and resolved it, I would love to hear what you did!