Hello,
Psychedelics are indeed a bit vague as a category, as psychedelic substances are often categorized along phenomenological critera. So some people may even include ketamine and MDMA as psychedelics. Most psychedelics however, seem to enact the seretonergic pathway, namely the 5-HT2A receptor amongst others. These are an evolutionarily new group of receptors and they seem to fullfill modulatory functions.
When researcher say 'psychedelics' this commonly refers to mescaline, 2-CB, LSD, Psilocybin, Aya huasca and DMT, because these all enact the 5-HT2A receptor and because these are the most well studied substances up to date. On the darkweb you will probably find many other psychedelic substances but these are considered too risky for human testing. The classic psychedelics have been around for quite a while, so they aren't considered that dangerous.
I would like to write a more extensive blog post about the network properties of the brain on psychedelics and explain how the effects can be broken down into physical terms such as 'entropy'. I would add that these are still only adressing the soft-problem of consciousness and not the hard-problem. Quantum explanations aren't being actively pursued in my field, these usually resonate more with philosophers who argue for panpsychism.
Thanks for your feedback!