The most prominent theory right now is that the fabric of the universe are tiny immaterial non-spacial and non-physical strings whose vibrations create what we call space, time and physical particles.
When you think about it, they have all the props of being spiritual.
I think your description highlights a sematic problem that crops up in physics talk about fundamental physics, about the meaning of 'physical' and 'reality'.
In quantum field theory, the particles which make up our human-scale reality are not really particles at all, but waves, excitations of quantum fields that permeate all space. Spacetime itself is thought likely to be emergent from quantum phenomena at a more fundamental level (e.g. entanglement). But I don't think there are many physicists that would say quantum fields are non-physical; rather, they represent a physical reality very different from our everyday experience. If fields are non-physical, then everything is non-physical - the distinction between physical and non-physical becomes moot.
String theory is a theory dealing with mathematical abstractions that may well represent a different form of fundamental physics, but the same reasoning applies.
Also, whatever name we give to the fundamental nature of what gives rise to our experiential world, the physical theories that describe it are mathematically rigorous, which means that although we may not be able to explain or understand all the complexity they give rise to, we can be confident beyond reasonable doubt what cannot occur under their regimes. By analogy with chess, we may not be good players or be able to explain or understand some game positions, but we know which moves are possible and which are not. If someone claims to solve a chess problem by moving a rook diagonally, we know they're wrong without bothering to check what they did.
It's not even necessary to explore the fundamental levels to have such confidence - the 'completion' of the Standard Model of particle physics (we know it's not the whole story, but we've completed part of the jigsaw) and the millions of empirical results that confirm it, tells us that the physics underlying everyday life at human scales is now understood. We know that we're made up of protons neutrons and electrons and we know the forces that can significantly influence them because that regime has been thoroughly explored.
Sean Carroll explains that claim and its implications at 34 mins into this video:
