Let's put it this way: relativistic mass is the equivalent of the mechanical and gravitational interaction of a body crossing our reference frame at a relativistic speed. If the mass of the photon in our reference frame was = 0, then there would be no effect of light pressure(solar sail) and the effect of light beam deflection (lensing) by the gravitational field. And do not put pressure on authorities (Okun, Einstein himself, etc.), the main authority in any science is a Natural Experiment. An authoritative uncle said to the Komsomol members a hundred years ago :” You will live under communism!”; they are already dead, but communism is still not there.
Let's put it this way: relativistic mass is the equivalent of the mechanical and gravitational interaction of a body crossing our reference frame at a relativistic speed. If the mass of the photon in our reference frame was = 0, then there would be no effect of light pressure(solar sail) and the effect of light beam deflection (lensing) by the gravitational field. And do not put pressure on authorities (Okun, Einstein himself, etc.), the main authority in any science is a Natural Experiment. An authoritative uncle said to the Komsomol members a hundred years ago :” You will live under communism!”; they are already dead, but communism is still not there.