Yes, it is hard to speculate how much time or years it will take before the quantum computer that can break entropy, but it is easier for the decentralized Bitcoin ecosystem to adopt quantum resistant algorithm.
According to the information I once read by Quside, the platform that developed new generation quantum technologies for connectivity and efficient computation. There's already a team working on quantum cryptography (like code based cryptography, lattice based cryptography) and post-quantum cryptography, which are said to be classical algorithms to combat quantum decryption, so I don't see any reason why it will be hard to have the creation of quantum resistant algorithms in Bitcoin.
You are talking about the creation of quantum-resistant algorithms but I am talking about a different thing: adopting and implementing that algorithm in Bitcoin.
It's not as easy as saying we created this quantum-resistant algorithm and tomorrow we are merging it into Bitcoin. That's not how it works. You are going to see BIPs with proposals to introduce the new schemes. Developers will have to review it, test it, get community feedback. Bugs and vulnerabilities would have to be looked for and corrected. All this can take a long time. Remember Segwit, the blocksize wars, and the aftermath? Remember Taproot and how long that took?
A decision has to be made if the new algorithm will be introduced through a soft or hard fork. Either way, there will be new addresses and scripts and changes to signatures. Everyone will have to move their coins from previous quantum-vulnerable scripts to the new quantum-resistant one. The bigger the change, the more drama, fighting, and resistance you can expect. Again, think back to the Segwit and Bitcoin Cash days.
And then all of the software we use with Bitcoin has to be updated to support the new quantum-safe scheme and new address format. That goes for nodes, miners, exchanges, etc.
Ok. Now I understand your stance. However, Bitcoin functions normally in a world with powerful quantum computers with no drawback, but the computer can be used in mining to increase the chance of finding a block early if used the Grover’s algorithm.
The computer is actually not a threat to Bitcoin, but it's a threat to the entropy used in creating the Bitcoin wallet we used, particularly those whose public key is already exposed online. Quantum computers can be used in the future to derive private keys from public keys and this is why the vulnerabilities need to be addressed ahead of time. Imagining someone stealing the Bitcoin you accumulated for years in one day?
About the decision to be made, I believe what we'll likely see is a soft fork for the implementation of quantum-resistant signature algorithm.