Can someone please explain to me why (according to decay of Higgs boson into 2 photons) Higgs boson cannot have spin $S=1$?
Just conserve angular momentum. If I have two photons on a collision course, their spin can either be aligned or anti-aligned, since photons must have spins lying on the same plane as their motion by virtue of their masslessness.
Then, you can either add one to one to get two, or you can subtract one from one to get zero. If you have a decay to two photons, the source particle(s) must have had a net spin of either zero or two.