Nomorebrightlights
I take an image of the screen
You won't be able to detect temporal dithering that way. You need a high-speed camera and a microscope.
it comes out with these checkerboard, wavy, or lined patterns
The photo is not available due to access rights issues. However, I would assume that what you're seeing is the moiré effect. It occurs due to interference between the pixel patterns on the screen and the camera sensor. There is nothing alarming about its presence; it's normal.
My MacbookPro is also PWM free, so that could be the contributor
PWM is the operating mode of the display's backlight lamps, and it does not depend on the signal source, i.e., the graphics card.
But dithering can occur both in the monitor itself and from the graphics card. Starting with El Capitan, a 10-bit output mode was added to the OS. I suppose this could activate temporal dithering on some Mac models. However, Apple doesn't specify this in the hardware specifications.
Please provide the full model name of your laptop.