You seem to forget that we currently do not have quantum computers powerful enough to brute force the public keys of a cold wallet to get the private keys. The current quantum computers we have now lacks the required qubit count, coherence time and the power to perform such a complex calculation.
It'll only take quantum computers with the IBM's 1,121 superconducting qubit processor to perform such a task as this is the only way to unlock the full power of quantum computing, and mate I don't think we have such computing power right now.
You quoted the image that the OP posted about Post-Quantum World.
I don't understand, what has what I said got to do with me quoting the image that the OP posted about Post-Quantum World? I'm kinda confused now...