What does "problem" mean in David Chalmers' "hard problem of consiousness"?

The physics of consciousness has become a respectable topic in recent years [1,2,3], at the interface between experimental studies [4] and theoretical constraints [5]. Here we address a problem in the philosophy of physics which is perhaps as central as the interpretation of quantum mechanics, and it is a question that the Austrian and Cambridge philosopher Ludwig Wittgenstein might have asked: In David Chalmers' "hard problem of consciousness" [6], what meaning can be assigned to the word "problem"? We argue that it is neither a scientific problem, because science is essentially just a map of the reality of Nature, nor a philosophical problem, since modern philosophy is essentially just a more profound version of clear thinking. It is instead a problem that in principle could be solved only through the combination of physics at the deepest level and a trans-human consciousness that is able to directly sample all the relevant aspects of that physics. In other words, the "hard problem" really is a problem and really is hard.

[1] Suzy Lidström and Roland E. Allen, “Consciousness as the collective excitation of a brainwide web—understanding consciousness from below quantum fields to above neuronal networks”, J. Phys: Conf. Ser. 1275, 012021 (2019), and references therein.

[2] Suzy Lidström and Roland E. Allen, “What is consciousness, and do we have free will?”, in G. Alexander et al., “The sounds of science—a symphony for many instruments and voices”,  Phys. Scr. 95, 062501 (2020).

[3] Suzy Lidström and Roland E. Allen, “Toward a physics description of consciousness”, Eur. Phys. J. Spec. Top. 230, 1081 (2021), and references therein.

[4] See e.g. S. Dehaene, Consciousness and the brain (Penguin Books, New York, 2014), and the papers cited in Ref. 3.

[5] See e.g. M. Tegmark, "The importance of quantum decoherence in brain processes", Phys. Rev. E 61, 4194 (2000).

[6] David Chalmers, "Facing up to the problem of consciousness", Journal of Consciousness Studies 2, 200 (1995).