I understand that QM without observers is unitary and conserves information. My problem starts when there is a measurement. It is my understanding that the measurement problem has not been adequately resolved. But does any of the different interpretations of QM (which exist mostly to address the measurement problem) have satisfactorily answered it? Some people claim that there is no such thing as "the measurement problem", but I have not heard any comments from them about information conservation. Other interpretations, such as decoherence, do not seem to address the measurement problem itself, or that is what some experts in the field say. The only interpretation that seems to address this problem is the Born "interpretation", but I put it in quotes because it is not just an interpretation, it is a theory itself because it adds additional hidden variables that evolve deterministically before the "collapse", and these might in principle be measurable, something that standard QM does not allow if it is the ultimate description of reality.
Thus, the question is: what is the state of the art answer to how information is conserved in QM?