I used the lamp from the specified source as a base, but I specifically needed a pyramidal shape for the lampshade. I created the design in Fusion and also included it in the files. The size of one side for the lithophane image is 150 mm in height, 167 mm wide at the bottom, and 90 mm wide at the top.

How did I make the side?
I created an STL blank using the service itslitho.com with dimensions 170×150 mm and imported it into Fusion as a mesh into the original lampshade design file.
Then, I tilted and adjusted it to match one of the sides of the lampshade in the original file and trimmed it using the Plane Cut tool with Full Type - Uniform along the inclined side edges, thereby achieving the pyramidal shape.
After that, I simply hid all other bodies except this one and exported it as an STL for further printing.

Original model https://www.thingiverse.com/thing:4949077