Quantum computers, 51% attacks...these are not new issues and have been discussed a lot over the past 16 years. But so far, those risks have been theoretical, they have never posed a real threat to bitcoin. So, no need to think too much and worry unnecessarily.

With the development of technology, quantum computers will develop  further in the future and may threaten the current bitcoin. But don't forget that Bitcoin is also constantly evolving, with developers working tirelessly to maintain and improve bitcoin protocol . So if at some point  quantum computers could threaten bitcoin, developers will have a solution to deal with it.