It doesn't work.

(Source: Wikipedia)

As you can see, the light does not follow a single path from the object to the projected image / camera sensor. Far an in-focus image, we put the object at S1 and the sensor at S2.

We can add another lens and project the image at S2 to a sensor on the other side (e.g. S4). We call the image at S2 an intermediate image.

For a coronagraph, we just add a mask at S2. That only works because the sun and the stars are in focus at the same time.

Usually, we do not have everything in focus, though. Out-of-focus areas will produce circles instead of points at S2, and different circles at S4. So, it is not possible to effectively filter out-of-focus areas at an intermediate image plane.*)

Another problem with such a filter is that the filter's structure is in focus. It will produce nice Moiré patterns when not 100% aligned with the sensor's pixels.

The only place to put this adaptive filter is in the sensor.

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*) There is one exception: You can do it for a very small aperture (like a pinhole camera), because there is essentially only one path from any point of the object to the sensor. But the image will be so dark already that you won't need any more darkening. Otherwise you'd need something like holographic technology.