Well, according to ACIM the dream movie is projected through one of 2 filters. These filters (which are also part of the illusion) give the dream a totally different meaning (=importance).
One is the Ego-filter and it gives the dream the meaning of specialness, time, cause and effect (guilt), attack and defense etc. This filter is very meaning-full.
The other filter is the filter of the Holy Spirit ("the right mind" or Jesus or whatever symbol of Truth).
This filter is the remembrance of Oneness and reverses all meaning and importance of the Ego-filter. Through this filter - in comparison to the other - everything has indeed to become meaningless for a while, before it gets the new meaning of Oneness.
This is just a very quick overview on how ACIM sees this and after studying nearly all the big philosophies and spiritual teachings from around the world, this was really a game changer for me.
About the topic of what is "real" and what is not, I can only tell you, that I have stopped asking me this question, because in my experience it doesn't lead anywhere but to philosophical mind-fucking.
For me, if you can see it, hear it, taste it, feel it or sense it, it's an illusion and has no reality on it's own. It's a symbol of the egos thought system and here to be forgiven (which is the courses version of "seeing the REALity behind it") .
Thank you for your comment! I really appreciate to take this topic deeper with you guys! 🙏