This is one of the most common questions which investors in Block Chain want to know while hearing about Quantum Computing.
There has been analysis from Price Water Coopers (PwC) , Deliotte etc on the same subject a couple of years ago(2019) precisly.
Please see the links as below
The article makes a bet on quantum computers capability.
"In the Bitcoin blockchain it currently takes about 10 minutes for transactions to be mined (unless the network is congested which has happened frequently in the past).
As long as it takes a quantum computer longer to derive the private key of a specific public key then the network should be safe against a quantum attack"
But as any observer in the industry can see , every now and then we are hearing break throughs about the progress of processing powes of Quantum computers.
Here is an interesting article about how Shors algorithm works in breaking the Encryption.
https://medium.com/asecuritysite-when-bob-met-alice/simplying-shors-method-3f0343b5a3c2
Like this one from Nagoya University which can increased the capabilities of a quantum computer around 10000 times.
https://phys.org/news/2021-08-worlds-combining-classical-quantum-supercomputing.html
Then we can imagine how much that 8 Hour boundary can shrink , it can be even minutes , if we extrapolate.
Here comes the importance of The "Right" post quantum cryptography algorithm.
The NIST (The National Institute of Standards and Technology) which is under United States Department of Commerce has been conducting a competition for selecting the suitable post quantum cryptography algorithm.
https://csrc.nist.gov/publications/detail/nistir/8309/final
The final candidates are the following from the article.
" The third-round finalist public-key encryption and key-establishment algorithms are Classic McEliece, CRYSTALS-KYBER, NTRU, and SABER.
The third-round finalists for digital signatures are CRYSTALS-DILITHIUM, FALCON, and Rainbow "
Most of the algorithms mentioned except Rainbow are new to me. Some version of linux uses Rain Bow tables , so has an some Idea about it.
So the message is very clear , the existing block chain can be compromised by Quantum computing and there is work in progress on the same on how to tackle it. But not only the block chain ,almost all other important information connected to the internet is also secured by cryptographic algorithms.
So untill there is an effort to tackle the challenges at national level or organisational level there cannot be guaranteed of saftey for the digital assets. But as we are aware cryptography is one of the "too geeky" subjects which majority of the folks in industry does not touch upon.
But to solve challenges like this there should be a brigade of core crypto guys who need to be nutured. Else There is a huge chance for surprise attacks in a say around 10 years time from now. And that is not a long period in case of strategic assets !!