Unless I’m profoundly mistaken, the D-D reaction has two equally-likely paths: an H3 nucleus and a proton, or a He3 nucleus and a neutron. As far as I know, D-D -> He4 is not a reaction that occurs with D-D; the secondary reaction of D with the H3 produced can generate He4, but it will also produce another neutron.
So in general, D-D fusion is not at all aneutronic.