Do high graphic FPS game companies use dual cameras for their game or a single cam only? If dual, then do they duplicate each mesh and assign it to the weapons layer for shadows and lighting or is their any other alternative method to it?
The triple A game company Valve, with regards to Team Fortress 2, decided to use 2 cameras to prevent viewmodels from clipping through the walls. The second camera renders on top of the first, and only renders viewmodels.
There are many advantages to this, which is that guns don’t clip through walls, viewmodels are physical objects in the scene (so it reacts to dynamic lighting), and you can easily see other player’s viewmodels, by switching to their camera view.
Optimization-wise, it’s not too terrible. URP in Unity offers camera stacking as an alternative, but using dual cameras is pretty common in FPS games. @bhaskarkumararya900