Having a single wavefunction just corresponds to the normal rule for the probabilities of events that are not independent. I still do not see any connection wi

Having a single wavefunction just corresponds to the normal rule for the probabilities of events that are not independent. I still do not see any connection with "quantum entanglement". Quantum entanglement is a very special case of the single wavefunction, not frequently encountered at large scales. In the general case that is valid for almost everything around us that single wavefunction differs only slightly from the product of many simpler wavefunctions that correspond to parts of the environment between which the interactions are non-existent or minimal.