Avi Loeb is the biggest conspiracy theorist among the physicist community. [scientificamerican.com] Even he exposes David Grusch for the fraud he is. The guy basically lied under oath in the house UAP hearing.
Weeeelll, first ya gotta prove there are dimensions with spaces in between...... this loon isn't doing it for me
Dimensions beyond 3D exist mathematically but are only theoretical. They aren't proven to exist at all.
I've heard it explained that they are like the 3 dimensions we have, all at right angles to all the others, but they didn't get "inflated" in the Big Bang so they are imperceptible to us. And yes, all theoretical, and the idea of interdimensional beings is nonsense.