How do I render a 3D object always on top of everything?

I tried using layers, camera distance, Z-Order but nothing.

Is to avoid cliping, like a gun in FPS games:

I know is possible render 2D on top or under 3D. But what about render a 3D object above any other 3D object? Any workaround? Maybe some FX on the layer or mask in some way? Any idea?

In godot it looks there is some shader that does the work: