You're using a Scene > Unit Scale of $0.001$ so the default values are way off—1000 times smaller than usual. For Eevee, set the Ambient Occlusion > Distance value in Render Properties to $0.2$ or something higher and you should see the occlusion:
Be aware that in your setup the "Render Pass" mode in the shading options dropdown is set to "Ambient Occlusion"
Cycles doesn't have that option of course, and doesn't seem to respond well to this difference in scale. If you switch to the standard Combined render pass mode, you might notice it does have a little bit of AO, but very weak. That's due to the
Ambient Occlusion node's default Distance value of $1.0$ in the shader. Multiply that with a bigger value as well and occlusion will pop up: