Here is a GPU based Flipping technique. I just used Graphics.Blit. Check the code below. I kept this answer here so I or anyone else can find a faster way to do it. So the Vector2(-1, 1) is what does the trick. It Scales in X axis or Y axis. So I just set it to Negative to flip.

Graphics.Blit(mainTexture, renderTexture, new Vector2(-1, 1), Vector2.zero);

To understand more about Graphics.Blit, check below link. Graphics.Blit