Color banding can be caused by the image, or by the monitor, or by the OS.
If the person making the image stretches the contrast, that can cause banding. e.g. you take the brightness levels from 48 to 176, and stretch them to cover from 0 to 255. Well, that doesn't create 256 brightness levels in the image, you've still got 128 brightness levels, they're just spread out more. So when the image is displayed, banding which used to be invisible because the shades were close, will now be visible because the shades are further apart. It can also show up in overcompressed images. There's not enough data to encode the exact brightness gradient, so the compression algorithm does a rougher approximation. Brightness bands are visible in this rougher gradient.
Most monitors use only 6-bit panels (64 brightness levels). They generate the extra 2 bits using something called FRC - they rapidly flicker the pixel between two brightness levels to simulate the in-between brightness levels they can't physically display. Some monitors do a worse job of this than others, and banding becomes visible.
If the color depth of the image doesn't match the color depth the OS is displaying, the OS may do a quick mapping which doesn't spread the brightness levels out evenly, resulting in bands. This has mostly disappeared with Windows 10 since it only supports 32-bit color (8 bits per primary color + 8 bits of transparency).
Looking at the image you've posted, my guess is you're seeing the first type. It looks like there are some compression artifacts visible in the bands, which would suggest the banding is a part of the image. But it could also be because you've got the monitor brightness/contrast set way too high. And stuff that's supposed to be an invisible gradient in the dark areas of the image are visible as bands because your brightness/contrast settings have stretched the dark part of the color space to the mid-brightness range (same as stretching the contrast in the image itself). A monitor with poor contrast ratio can force you to do this - if you set the brightness so the light areas are comfortably bright, the dark areas become too light because the monitor's limited contrast ratio can't do any better. It's one of the reasons you should always check reviews on a monitor or see it in person before buying it.
Edit: There's a long-running Nvidia bug/feature which could cause this type of problem, but I thought they'd resolved it many years ago. Might be worth checking out. (The "full" color range would result in images having too much contrast when the computer is hooked up to a TV via HDMI.)
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