

Quantum computers only provide a significant advantage at breaking a very specific class of asymmetric ciphers (those where the trapdoor function is either based on the discrete logarithm problem or the factorization problem) which we already have replacements for that are quantum-resistant (the trapdoor function is replaced with one based on the lattice problem). If quantum computers became a serious threat, it would not be difficult to just swap out those ciphers. The main issue would be people who have collected encrypted messages and held onto them with the hopes of cracking them in the future.
Quantum computers will always exist as a coprocessor, like a GPU or an NPU. You cannot run an operating system on your GPU either. Your GPU is worse for a lot of general purpose tasks your CPU can do, but it excels at very specific kinds of tasks, and so your CPU delegates those specific tasks to the GPU. That is how quantum computers work in practice, they are never stand-alone computers. They are always attached to a classical computer that delegates tasks to it. They won’t ever replace regular computers. Even if in the distant future they manage to build quantum optical chips that run at room temperature at can be made consumer-affordable, they will just be sold as QPUs which you would install into your regular personal computer if you need one.