As per the latest, Google has reached Quantum Supremacy. Meaning it could potentially decode an entire blockchain and...
YOUR PRIVATE KEYS...
Blockchains are secured through elliptic curve cryptography (ECC), just like encrypted user data and website traffic. Now the issue is that ECC is NOT "quantum-safe" meaning that a quantum computer could theoretically decrypt a user's private keys and forge transaction signatures.
Is this the end of Crypto?
I don't think so, but I'd love to hear your opinions too! (Especially the opinion of a cryptographer)

source https://www.coindesk.com/what-googles-quantum-supremacy-means-for-the-future-of-cryptocurrency