i just now figure out that i have made one major mistake while making normal i.e. i have kept normal maps colour space setting in blender as sRGB is there.
and I have also deleted my high poly version .is there any way I can get those amazing normals in non colour mode.
Never realised I had this exact problem, not with Unity, but after a bake when I was still fairly new to learning. I never did figure out what was wrong with it and moved on. Later bakes worked properly. I just opened my old file that I knew had this issue and sure enough, my normal map was set to sRGB Color Space.