I hadn’t looked up what Michio Kaku had said about quantum computing before, but it does not look well-regarded.

“His 2023 book on Quantum Supremacy has been criticized by quantum computer scientist Scott Aaronson on his blog. Aaronson states "Kaku appears to have had zero prior engagement with quantum computing, and also to have consulted zero relevant experts who could’ve fixed his misconceptions””

I’m hardly an expert on the subject, but as I understand it they have some very niche uses, mostly in cryptography and some forms of simulation.