macbook thermal problems

I have a macbook air 2018 edition which has bad thermals from long usage which makes my screen flicker as a thin line on the very bottom edge of the screen. If my warranty is over, will apple still fix this issue for free? Because I do not understand why using a computer for a long time say max 5 hours a day will cause damage to the hardware. Edit: here is a picture of my issue  There are these lines on the bottom edge that was not here yesterday, but here when I turned on the computer this morning.