I can see the line....but why would they photoshop it?
Makes no sense.
It's not photoshopped. This is a common photo element used on advertising photos by creating reflections to show the surface, especially when a seller has multiple variants(like matte vs polished surfaces).
For example, look through Apple's iPhone variants and you will see the reflections depict the surface details of each iphone. Speficially, if you look at the iPhone 11 Pro, the back glass is has a matte finish, while the camera housing has a polished finish. The advertised photo shows a clean line on the camera housing glass to depict this difference between the two surfaces.
There's nothing complicated about it.
The back of the iPhone SE is glass.
A straight reflection against two contrasting lit backgrounds will give you that exact reflection.
It's just an advertisement!
Same with the Macbooks.
FYI: NONE of the advertised Apple devices include photoshopped images. They are true photos, with true lighting, and real reflections.