bitcoin has many different parts

sha hashes are binary
ECDSA are vectors

quantum computers are not really going to do much harm to binary, because what quantum needs to do is to while calculating outside the realm of binary, it needs to ensure the result and method can be solvable by a binary system. thus limiting quantum's capabilities

however vectors are at risk. quantum computers can solve vector issues much faster
its been suggested that quantum computers can solve a sha only 2x as fast as a binary computer but solve a vector 65536 faster

and with quantum computers only having half a dozen units at a low processing power.. compared to the combined bitcoin network of ASIC power... quantum computers has no chance of bruteforcing sha hashes any time soon

.. but ecdsa has some risks.. given enough time

Well theoretically, quantum computers could derive your private key from your public key. It's one of the reasons why reusing addresses is discouraged. If quantum computers were a thing, they could probably get access to any address that has ever sent a transaction.

As for its effects on Bitcoin, it's really hard to tell. It's not guaranteed that the first quantum computers will necessarily have enough power to break Bitcoin's cryptography. It could take a while even then. If they happen to break through before Bitcoin shifts to quantum proof cryptography, then it's likely toast.

Then it might be possible to update the code against the quantum computer, and for years to come, who might have been.