quantum computing can be a threat because it will be able to break encryptions which could put documents and data in danger it could be a threat to all kinds of industries such as transportation a quantum computer can get into aviation systems which could serve dangerous to the pilots and passengers
however since we are in a forum about cryptocurrency it is normal that we focus on what quantum computer can do against crypto and what can we do to avoid such cases
Well, if someone can break SHA-256 right now, we don't need to worry too much about BTC future because we will have many more concerns then. Bank accounts, national security, data security... will be the first things attacked and cause extremely large damages, not stopping at the marketcap of BTC.
Currently, many new encryption algorithms have been developed and they are quantum-resistant, so we can rest assured and focus on investing. We have already had AI-trend, so quantum-trend can completely explode in the future and the crypto market will also have many more projects in this field. We should think about being ready to profit from the quantum-trend in the future instead of worrying uselessly about the risk from it ^^