I have been obsessed with this question for a while.
Imho you can not do this with built-in filters or drop shadow on Ps, or Gimp as far as I know.
Let me analyze what this shadow is about.
A. You have a triangular zone with a gradient, where on the right corner you do not have any blur, because the object is touching the floor, so the shadow is sharp, but on the far side you have a lot of blur because the part of the notebook that is casting that part is far from the floor. This indicates a softbox as iluminant.
B. You then have a normally blurry shadow.
C. But this shadow has a logarithmic-ish decay.
The main obstacle is point A I tried masking, making a tiny triangle, and making a transparent gradient (That could work but is tricky), using motion blur, and zoom blur.
But as I am a fan of using vectors, here is an option. The image on the right is the original reference. I used Corel Draw, but the process should be the same on Ilustrator.
I have the cover pasted as a new object on top of my shadow shapes.
I constructed 2 shapes, red and purple. But a very important thing is the extra node on the purple shape. It is highlighted with the green lines. This node will translate to the corresponding vertex on the red shape.
And I mixed the shapes. https://helpx.adobe.com/in/illustrator/using/tool-techniques/blend-tool.html
You can notice how this extra node produced triangle A.
There is an extra feature on the original shapes. The rounded corner of the top-left is to smooth that part of the shadow.
Now I converted the combined shapes to a bitmap because I need the effect to be fixed, and I added a transparency. I am aiming for the darkest color of the shadow to match the tone of the target image. I could have colored the original shape this light gray, but I need the full tonal range of the image for the next step.
Now I edit the curves to give the "logarithmic-ish" decay on the tones of the shadow. This curve is very simple because I used the full tonal range from black to white.
The result is decent. We have triangle A, gradient B and the proper fall of C.
It needs a bit of tweaking to match the original. But the effect is more consistent than only using a drop shadow. That effect would imply a floating flat cover instead of a notebook on the floor with volume.
For a more realistic shadow, I would use a 3D program with a physically correct render. I could then import the shadow as a layer in case I need it as a template.