Making a clay render is a nice way to show case that your totally realistic render was, in fact modeled in Blender. Here are the steps to convert this...

...into something that looks like this.

1. Create the Clay Material

Use any mesh to create a new material that uses a simple Principled BSDF with a flat white color.

2. Override all materials with it.

In View Layer, go down to Override > Material Override and select the aforementioned clay material.

3. Show the Wireframe

In Viewport Overlays check Wireframe. Now in Cycles, render the scene; You'll notice that the wireframe isn't present in the render which is expected, it's only visible in the viewport as an overlay. However you will need the render itself later.

4. Capture the Wireframe

Whilst in rendered view, go to View > Viewport Render Image. This creates a render of just the wireframe against a transparent background, save this. One would expect this option to capture the wireframe against the render itself but for some reason this doesn't work in the rendered view for Cycles. This option works perfectly fine if you're in solid view or material preview so you can simply stop here if you don't need the realistic lighting. Otherwise continue to the next step.

5. Combine the Render with the Wireframe.

Using the render made in step 3, go to the compositing tab and create the following node setup.

Create a Color > Mix > Alpha Over node. Create an Input > Image node, select the wireframe and connect it to the bottom slot of the alpha over. Finally connect the image output from the render layer into the top slot. This results in the render at the top of this post.