I don't know where you're getting this, but thermodynamics and kitty-dynamics don't apply here. Schrödinger's cat is a thought experiment to illustrate the quantum/classic divide. His actual work is an equation that very accurately describes how the quantum state of a physical system changes over time, and that's what's really relevant here.
Quantum computers work, we know this. They work at the scale we have now (maybe 48 logical qubits, depending on who you trust), and they work just the same at the scale of 2,000 logical qubits, which is what's needed to crack Bitcoin private keys. (Unless we further optimize, in which case it'll be fewer.)
Scaling the sheer number of qubits does not imply "getting bigger" in the sense of lessening quantum effects. Basically increasing the complexity and number of these isolated quantum units is not allowing the system to become a large or "hot" classical object. The system remains fundamentally quantum.
