Impact at the edge of screen created microscopic crack. Thermal change caused the crack to spread. It happens all the time with vehicle windshields.
It is possible many or most of the reported screen cracks are due entirely to thermal changes. The M1 MacBook displays are made of glass . Glass is a poor thermal conductor and rapid changes in temperature will create stress fractures in the glass that will eventually crack. When heated, thin glass begins to crack. Let's say, for argument's sake, the OP has their desk in front of a window. At night, temperatures go d…
Perhaps Apple should have done so, knowing their users might expose their laptops to sunlight...