Our reality is fully conceptually knowable, but Laplace's demon is dead. Mechanistic determinism cannot work because our epistemic view of the universe is fundamentally limited. No measuring process can overcome it. This is demonstrated with the success of the uncertainty principle.
This is not incompatible with the viewpoint of a deterministic universe, however. In fact, the conclusion it tells us is philosophically congruent to the solution of the halting problem, the discovery of chaos theory, and the godel incompleteness theorem. All of these things tell us that, even if all the physical laws are known, we cannot know everything