The U.S.S. Discovery Spore drive, is it complete nonsense or is there a scientific theory I’m unaware of?
Both, since it relies quite heavily on Star Trek's Signature Subspace Science, and there's no real-life equivalent for it.
The spores are from the mycelial network, an organism/structure that exists in a subspace domain, and like subspace, is spread/connected throughout the universe/multiverse. The spore drive shifts the ship into that subspace domain, and uses the mycelial network to route the ship to the appropriate destination.
The closest things that might apply is the hyperdrives in the Hitchhiker's Guide to the Galaxy, or the space-folding drives in Dune, where you have a spanning extradimensional network that you can use to get to your destination, as long as you can find the right set of routes to get to where you want to go.