How to clean up a mesh in order to export a freestyle vector for a 3D engraved lamp? I'm trying to create meshes for a 3D illusion lamp that is made through laser engraving acrylic. Like the one on the below picture.

As I'm new to 3D modelling and I mostly do architecture stuff or furniture, I really struggle with organic shapes, which are most of the requests that I get now. As an example, I downloaded this model and as you can see below, the mesh is way too dense for my purpose.

I tried to decimate the mesh but the result I get is not what I'm after as it ends up being triangles rather than a tidy mesh like the shark above.

Is there a way to get a similar result cleaning up the mesh? Or is the only way modelling it from the scratch (in which case I would have to give up as I can't model such a complex shape).
All the freestyle  vector export I can handle. It's the mesh that's my problem. I would greatly appreciate any suggestion.
Thanks!
Go to the Object Data Properties tab, and under Remesh, set the mode to Quad and click Quadriflow Remesh

Set the target number of faces (I set 20,000 - eventually you will lose an undesired amount of mesh resolution, so don't go too low) and click the Ok button.

The result (at 20,000) looks like this:

The mesh looks even better at 10,000, but you will begin to get some artefacts if you get too low, so I suggest somewhere between 12,000 and 20,000 for your final result.