Quantum computing is not "growing rapidly", it is at best "fast approaching" (and even that is doubtful). There is no quantum computer that does any kind of useful work today at all * - the biggest accomplishment of any quantum computer to date has been to run a simplified version of quantum factoring that calculated the prime factors of 15 are 3 and 5, if I remember correctly (maybe it was 21 = 3 × 7 actually?).
Also, the blockchain is not encrypted, it is cryptographically signed. Any clients "decrypt" it all day every day, that is how you verify it. The security comes from making it hard to find a hash of a block that has the right structure. I don't think it is known whether any quantum algorithm could improve significantly on this problem (there might be a small improvement from using the quantum O(sqrt(n)) Grover's algorithm instead of the classical O(n) searches, but that's not hard to work around). Note that quantum computers are only known to be exponentially faster at a handful of very specific problems, not in the general case. While this is not established fully, it is considered highly likely by those in the field to be the case.
* there are some computers that implement specific quantum algorithms that are sometimes called quantum computers, but those can't do the more interesting algorithms that could break encryption.
Also, the blockchain is not encrypted, it is cryptographically signed. Any clients "decrypt" it all day every day, that is how you verify it. The security comes from making it hard to find a hash of a block that has the right structure. I don't think it is known whether any quantum algorithm could improve significantly on this problem (there might be a small improvement from using the quantum O(sqrt(n)) Grover's algorithm instead of the classical O(n) searches, but that's not hard to work around). Note that quantum computers are only known to be exponentially faster at a handful of very specific problems, not in the general case. While this is not established fully, it is considered highly likely by those in the field to be the case.
* there are some computers that implement specific quantum algorithms that are sometimes called quantum computers, but those can't do the more interesting algorithms that could break encryption.