You are labouring under some misconceptions.
Quantum mechanics is deterministic. It describes each system in terms of observables that evolve deterministically according to an equation of motion. However, these observables describe multiple versions of that object that can interact with one another in quantum interference phenomena. Objects interact with one another and the environment in such a way that they form layers each of which approximately obeys the laws of classical physics. The whole set of layers is called the multiverse:
The applicability of classical equations of motion on a macroscopic scale is a consequence of quantum mechanics. Distinctively quantum mechanical effects are more difficult to detect in macroscopic objects as a result of interaction with the environment, not because quantum mechanics ceases to apply to macroscopic systems:
Since multiple versions of a system can interact to produce a given outcome there is, in general, no such thing as which of those versions produced any given outcome. So while it is possible to predict how the multiverse as a whole will evolve it is not possible to predict what you will see because there is no single fact of the matter about that.
Explaining the results of experiments often requires explaining the behaviour of macroscopic objects using quantum mechanics. For example, the explanation of the EPR experiments requires describing "classical" systems in terms of their quantum observables: