Leaving aside quantum physics for the moment, there are at least two general ways in which indeterministic and deterministic rules can co-exist at different scales.
The first way is when deterministic laws emerge at some higher level, and can be explained from averaging fundamentally indeterministic events. You can see this happen in most views of classical statistical mechanics, where microscopic events can be treated as fundamental and random, but when the number of particles gets very large, macroscopic rule-following behavior can emerge, like the heat equation.
A totally different perspective is when deterministic fundamental rules end up looking indeterministic in practice. Imagine that everything is fully determined, given both some fundamental rules and also some "input" data (say, an initial state). As we analyze events in such a situation, our ability to make perfect predictions depends on perfect knowledge of the system and the inputs. If we don't know something precisely, we have to drop back to a probabilistic/indeterministic viewpoint, assigning probabilities to the unknown parameters. If new inputs keep coming into the system, of which we continue to have imperfect information, then the rules of the universe, in practice, look indeterministic. One example here is how indeterministic Brownian motion can be derived from fundamentally deterministic laws with unknown noise/inputs.
Okay, so which of these is most analogous to quantum theory? That's an open debate in quantum foundations, which no evident resolution in sight. The first perspective above would tend to be aligned with spontaneous collapse models, and the second perspective would be more aligned with Bohmian mechanics. And it's possible that both are happening at different scales, that deterministic fundamental rules look to us to be indeterministic, because of lack of knowledge, but then those indeterministic rules get averaged out to make deterministic classical rules at some large macroscopic scale. (The Everettians would fall in this two-stage category, and presumably the Bohmians as well.)
And just to add one more wrinkle to all this, our traditional viewpoint of what should be considered "fundamentally deterministic" might be too restricted in the first place. For example, Emily Adlam has argued that a universe which depends on both the past and the future could be considered "globally deterministic" in a well-defined sense. And since we don't know the future, that "global determinism" would inevitably look to us like local-indeterminism. This view would work well with future-input-dependent interpretations of quantum theory.
But back to your question, yes, it's possible that we're wrong about "all this indeterminism" existing in our fundamental laws. Certainly many quantum physicists will tell you that there is no indeterminism in the fundamental laws, at least if they had a solution to the Measurement Problem. But it seems extremely doubtful that we're wrong about needing indeterministic rules in practice, because of that second perspective, combined with all the microscopic details that we don't know.
