It's untestable by the definition of the term "superdeterminism" and the meaning of what it implies -- just as “1 + 1 = 3” is something that cannot make sense,

It's untestable by the definition of the term "superdeterminism" and the meaning of what it implies -- just as “1 + 1 = 3” is something that cannot make sense, by the very definition and meaning of its symbols. But this doesn't make it wrong. Superdeterminism is a very neat way of resolving physical paradoxes, such as the Wigner's Friend paradox: Any experimenter’s decision to take a measurement of a certain physical phenomenon is predetermined by events, so the experimenter can attain no outcome but the one he does eventually attain, and nothing is in superposition. Neither Heisenberg's uncertainty principle nor Bell's inequality render this condition impossible, as Bell himself was well aware.