Is there a metaphysics that seeks to explain what might exist beyond quantum physics? Beyond what we can know about quantum physics? What are the laws of reality beyond those we were able to find through quantum physics?
There are various attempts. Some are called interpretations of quantum mechanics. Like there are hidden variables and many worlds. Both are attempts to find a realty behind the ordinary theory. Both are attempts to understand the behavior of the wave function but the many worlds theory is mainly concerned with the non-unitary collapse of the ordinary wave function. The hidden variable theory is concerned about the Nature of the wave function in general. It says that the wavefunction itself consists of hidden variables and that when the wav function collapses a real collapse of these variables takes place. The Nature of these variables is a bit unclear because the variables are, well, hidden. They surely don't act as the particles they accompany.
And there are more interpretations. A real theory to explain quantum behavior (why there is this seemingly inherent probability in Nature) is not found (though hidden variables come close).
Quantum field theory may offer a solution though. There is something called second quantization but that's misleading. The things quantized are different (particle fields instead of particles). Particles (viewed as points but this might even the source of many problems, but never mind) travel along all (litteraly ALL) trajectories at the same time. Every trajectory has a certain probability amplitude. Even backward in time. And this behavior gives rise to a wave function. This is a quite deterministic theory (like the many worlds and hidden variables). But it still makes use of probability amplitudes.
It's the question if an even more deep theory can be found. Hidden variables come close and they might be there in the structure of spacetime (on a microscopic level). The Dutch physicist van 't Hooft is an advocate of a purely deterministic view(he is a member of the physics site so you can look him up).
It depends on what you mean by metaphysics. The popular definition of metaphysics deals with the supposed existence of phenomena experienced by humans which have no conventional explanation, like for example UFO abductions, ghosts, haunted houses, witchcraft, telepathy, telekinesis, spoonbending, and so on. Metaphysicists in this arena have nothing to contribute to, for example, unifying quantum mechanics with general relativity.
But to be more generous: let us instead assume that someone in metaphysical philosophy invents some general philosophical principle which they assert establishes the ground rules for the structure of whatever goes beyond quantum mechanics and the Standard Model of particle physics- providing an overarching epistemological framework which any description of the functioning of the universe is logically obligated to adhere to. Then he or she asserts that this principle should guide the search for physics beyond the so-called Standard Model.
Is that philosopher then going to dauntlessly stride into the offices of CERN and say to a staff researcher, "Now see here my good man, my General Principle Of Metaphysics very clearly and unambiguously states that the Higgs Boson cannot exist, and therefore anyone who wishes to extend physics beyond the Standard Model by exploring the Higgs mechanism is wasting their time"?
This is not likely to be effective. As such, it is the physics community, and not the philosophy community, that is best equipped to answer the question of what exists beyond quantum mechanics and the Standard Model.