Hi guys!
I don’t know why, but if I put a second camera into my scene, then it reduces the frame rate significantly. Even if it does not render anything 
The camera’s Clear Flags setting is set to “Depth Only”, and it is rendering over the main camera (its Depth property is higher then the one of the main camera).
However, if I switch the rendering path from default (forward) to deferred, the frame rate becomes as high as it is without the second camera.
I looked into the frame debugger, and it seems that the main difference is that the forward rendering uses a render texture for combining the views of two cameras. The impact of the second camera (which renders nothing:)) is emphasized with a rectangle on the screenshot.
Does anyone have an idea, why forward rendering with two cameras is so slow? Maybe there is a way to improve its performance?
You never stated what version of Unity your using (BuiltIn, HDRP, URP), it looks to be HDRP, IF it is, you cant use more than one camera in HDRP, or your performance will tank.