> not even the core part of Bitcoin blockchains, which are not vulnerable to quantum computers

Um, what? Shor’s algorithm can take the public key of a wallet (present on any outgoing transaction in the ledger) and produce its private key. So now you can hijack any wallet that has transferred any Bitcoin. Notably only one successful run of the algorithm is needed per wallet, so you could just pick a big one if it takes weeks.

It probably wouldn’t help you mine in practice, sure. Technically it would give you better asymptotic mining performance (via Grover’s algorithm) but almost certainly worse in practice for the foreseeable future.