Let's get the processor model numbers correct. You are mixing i7-6600U, and i7-7660U . Which one do you have?
The i7-6600U has HD 520 graphics, and the i7-7660U has Iris Plus Graphics 640.
No real mystery here.
Ah, thanks, that's correct. I was mixing 6600U and 7660U.
Problem solved. The issue was between the chair and the keyboard!