The wave function of the universe defines all physical possibilities. Quantum decoherence is what transforms the wave function into specific versions of physical reality. This is an interference effect that alters the structure of the wave function, producing essentially classical states. This is what transforms the amorphous fundamental wave function into an ordinary world of the sort we are used to.
It has been proposed that this phenomenon explains the whole problem of the collapse of the wave function, and thus resolves the measurement problem. However, as stated by the physicist Guido Bacciagaluppi, in his article The Role of Decoherence in Quantum Mechanics:
Unfortunately, naïve claims of the kind that decoherence gives a complete answer to the measurement problem are still somewhat part of the ‘folklore’ of decoherence, and deservedly attract the wrath of physicists (e.g. Pearle 1997) and philosophers (e.g. Bub 1997, Chap. 8) alike. (2012)
In any case, this cannot be the whole story because different individuals would be in the same physical environment on that basis, and as shown by the experimental confirmation of the Wigner’s friend concept by Proietti et al. (2019) they are not. When it comes to explaining Wigner’s friend, only Everett’s stated solution works. As he states, although all the possible versions of the world do happen, it is only in experience that one single, specific version of the world exists.