Unfortunately I work in cryptography, and breaking our algorithms is one of the tasks that requires the least number of qubits. And that doesn't depend on having a desktop quantum computer either, but only that a single state actor anywhere has a sufficiently large quantum computer.
I'm a bit bitter that physics handed us this magical tool, and the best we managed so far is using it to invalidate decades of security research.
You only need a few thousand error-free qubits to implement Shor's algorithm for 256-bit Elliptic Curve Discrete Log, that will for instance break nearly all crypto. The "millions" is trying to account for the several orders of magnitude error correcting overhead.
Sure, I just don't think error-free qubits are a thing (or will be in the future). I don't think anyone seriously expects quantum computing to work without error correction.
The difficulty of adding qubits increases super-linearly with the number of qubits (especially because of communication delay vs time to decoherence) , so "only" a few thousand is already very optimistic. Worse, the idea of "error-free qubits" is essentially like cold fusion - you can say the words and we understand what you mean by them, but they don't describe anything that can exist in practice.
That's from three years ago, and for error-corrected RSA breaking. ECC has keys an order of magnitude smaller, and minimizing the number of quits to run Shor's is a hot area.
And compared to other uses (quantum AI anyone?), it's surprisingly compact.
It's rather easy to produce qubits and place them in a box. The hard part is to make them interact with each other in a controlled fashion thus, adding one qubit to a large system is substantially harder than adding it to a small one.
The only true benchmark is a factorisation of numbers. Number 21 has been factorised with nudging. Let's wait for a number 45 in the coming next decade.
I'm a bit bitter that physics handed us this magical tool, and the best we managed so far is using it to invalidate decades of security research.