> The only exception seems to be Quantum Computing

Yet so far it failed to do any useful work, correct? As I understand it, even the recent "quantum supremacy" results were about performing a humongous number of useless computations.

It would be funny if this turned out to also apply to quantum computing. Ie while we can build a quantum computer, we can't actually find any productive problem that calculates faster than a classical algorithm.

QC would turn out to be the biggest bust in physics (after string theory of course).

So far yes, but we should be able to in principle for a few kinds of problems.