In my opinion, it is necessary to distinguish between directly observable and unobservable energies. Baryonic, leptonic and photonic energies are directly measurable, but not the dark ones:
That is, the energy generated during the big bang is mostly "vacuum energy" of the spacetime, which is only a geometrical gauge to measure actual magnitudes. If general relativity is imposed to be valid also at a cosmic scale, "dark energy" and "dark matter" appears to be necessary new parameters, but they could be fictitious magnitudes by overfitting.
It was all conserved and is still present, either as the mass of the particles created from that energy, or as photons moving through space (or if beyond the Observable Universe, hidden by the Cosmic Microwave Background Radiation). However, the energy contained within the Observable Universe is much smaller than the original energy, part of it being lost by being beyond the CMBR, and part of it by the shifting of its originally very short wavelengths to much longer wavelengths as a result of the expansion of the Universe. As a result, the energy in any given region is continually decreasing, even though the total energy remains the same.
It is unknown exactly that the existing of the Universe is due to Big Bang. Moreover, the concept of the Big Bang is found on the theory of homogeneous isotropic Universe. This theory is found on the model of homogeneous isotropic Universe, which does not allow gravitation and rotation of the space of the Universe. It follows from this concept that the space of this Universe does not gravitate and rotate. But it is known that the Universe gravitates. Galaxies, stars and planets possese gravitational fields.
The problem is that we do not know how the energy that created the universe came about.
We do not know how or why “dark energy” involved in cosmic expansion works. On the face of it, the resultant increased separation between objects is adding to the gravitational potential energy of the Universe, but where does it come from in the first place?
Either three is a huge reservoir of energy somewhere, or it is being created.
A more realistic description is given in my first book. It explaines for instance how the supermassive objects in the center of he galaxies come about. Big Bang gives no such explanation
Our Universe as all its bodies is created by the energy of the Time. Moreover, we cannot be sure that it is just one sample. Our Universe possesses own time of existing, and the times of all its bodies are the parts of the time of our Universe. In other words, the space of the Universe is created as a Fractal , where every its body is a fragment of the Universe. The fractal of the Universe is the materialized state of the Time of the Universe. Russian scientist Shnol proved experimentally that time possesses a fractal structure. It is the Time of the Universe that is the Energy of the Universe which want to find many scientists of different specialisities.