Your dreams and imagination evolved as a view into another universe. As with the current beliefs, you cannot decipher technical information – no words in books, no details of how devices work, so even if you can describe things you see from another place, you could not reproduce a working version.
Now how do you convince others that the things your are seeing are really happening without being labeled insane? And how could you use this information to benefit yourself or others? Take a peek into the multiverse to see how other versions of yourself have solved these problems…
There are a few ways it can be proven.
If the parallel universes are different versions of our own, I can use them to get information I couldn’t get in my own universe. For example, if it’s a universe where North Korea has an open border policy, I could walk in and observe my surroundings, then end the dream and describe things about North Korea nobody knows about. Though this is not super hard proof.
I could venture into the parallel universe to get a better understanding of physics, and people in my universe would know something is up because I came back knowing about how things work that the average person could never know. Though, again, this is not super hard proof.
I can play Marco Polo with other sleepers from my universe to see if I can find them in the parallel universe, using a system of identification that cannot be impersonated if any entity tried. This would be hard proof, but it would require that people end up in the same parallel universes.
I think most of what you’re describing would require focused lucid dreaming, and with #3 it would require that you meet others who are also lucid dreaming? Sure that can be done, but #2 requires you to bring back critical details that the right brain just doesn’t seem to be able to handle. This does give me an idea that might get around that limitation though – what if you could remember images of artwork created in other realities? Basically steal their classic masterpieces (of course I’m still limited in that I cannot paint). And curiously, #1 sounds very much like the descriptions of remote viewing that are supposed to be proof that ESP is real but always fall apart because some details are wrong – exactly what you would expect from an alternate reality though…