Make no mistake, quantum computing is a threat towards anything secured by public-private keys. The amount of qubits required to break ECDSA is above a thousand and currently, there isn't any quantum computers that is close to that, without running it for longer periods of time and without errors.
It's not hard to design a new algorithm to secure the signatures but the harder part should be about securing the addresses with coins and were P2PK.
There's isn't any quantum computers close to that, because quantum computing does not yet exist lol. Quantum computing is a threat, hackers are a threat, government regulation is a threat etc etc. There's plenty of threats to bitcoin/cryptocurrency and it's ecosystem, but that doesn't mean they can't be easily neutralized. As someone else in here already stated, they will simply build in a defense, with quantum computers or once we know how they full operate, they will be able to build in protection. The beauty of code, it can always be upgraded.