Deepest inside a neutrino we do not find matter, we find energy, same as every other presumed particle with apparent mass. “Matter” as we understand it does not require solid material to have mass. After all, energy can imitate matter with mass. Look at the photon. It can act as if it has mass while it does not. It can exert pressure while still undoubtedly being pure energy “congealed” to act like matter with mass.