3D pixelation is just using low resolution textures and setting the nearest filter in the project settings, according to the link above.
But 3D in Defold is a wider topic. You can take a look at this or this thread.
Since you are specifically interested in pixel 3D, if this example is what are you looking for then take a look at the demo that comes with the trenchbroom extension.
Unfortunately, your picture didn’t load, so it’s not clear what type of 3D we are talking about.