You don’t see objective reality objectively

For example, I could be a brain in a vat, being fed sense signals through wires that is making me feel that I live on this blue green rocky planet revolving around a big ball of fire. If so, "I am a brain in a vat" is the objective reality, even though the "I" inside this simulated universe may never be able to perceive the true reality.

It's true that we can never be 100% sure that our sense signals are truly objective and not something emergent (spacetime of our universe) from a more fundamental reality (say, brain in a vat). Then what should we do? I believe the best thing we can do is to follow the data. As long as we continue to observe that our universe is consistently and precisely obeying the physical laws we have discovered, we can axiomatically assume that we do live in objective reality. As we dig deeper, we may make new observations indicating we exist in a Matrix after all. We'd then have to update our mental models accordingly.