Explain Like I'm Five

I'm familiar with that specific interpretation of quantum mechanics. It's not relevant to the question, and it is a complete misinterpretation of Schrödinger's thought experiment, both its concept and its purpose. He thought that the indeterministic view of quantum mechanics was wrong, and he used the thought experiment to demonstrate how ridiculous it is by bringing it into a macroscopic scale. It's become a lie for children that omits many factors, like what it means to "observe or measure" a system.

You're missing the essential element of this thought experiment - the poison gas canister in the box which releases the gas when an atom decays. That atomic decay is a quantum event that cannot be predicted even if one has perfect knowledge of the atom concerned, and in fact whether it has actually decayed or not only becomes real when it is measured ie observed. Thus, according to this experiment, the cat is simultaneously alive and dead at once, up until the box is opened and an observation made.

If you don't have that atomic decay, then the cat's health is merely unknown - it is either alive or dead, not both at once, but the scientist simply doesn't know which.