The overriding stylistic discipline is often referred to as “NPR”, or non–photorealistic rendering. NPR isn’t limited to a specific style, but rather a goal which is to look more like an illustration than real life.

As with illustration, there are many approaches, and your example of The Witness is an interesting one as it combines abstract, flat textures with a hyper-real lighting model that exaggerates the effects of bounces and translucency. It’s very much its own style, while being an excellent example of NPR art direction.

Maybe cel shaded is what you're looking for. Basically rounding colours to the nearest pallete color so that lighting looks cartoonish instead of uncanny.

"Stylized" is the more recent term used for it.

I feel like the most common name is "low-poly".