Quantum Computing is simply computing using circuits much smaller than electronic circuits that are used now. To achieve "quantum" computing they must use something as small as individual photons or ions. In order to build quantum computing "chips" using photons or ions, what we know of as lithography has to be completely reimagined. Lithography Is how they have printed computing chips using ultra fast, small, and powerful lasers to etch the circuits into the silica material. Doing this for individual ions, or photons, is an entirely different challenge at any type of scale. All scientists have been able to achieve is controlled, small, and unreliable, results using photons or ions.
Currently, in my opinion, some supercomputers, AI, and social engineering attacks are far more of a threat to encryption than "quantum". I believe "quantum" has been used a a PSYOP to keep prices of BTC low so they can aquire.