I'm not sure. 6ghz is around 2^61 CPU cycles in 12 years. I.E. basic CPU instructions; counting, not computing a cryptographic hash. Otherwise, where is the cluster that's bruteforcing ~122 bit cryptographic hash collisions in minutes?
For cryptographic applications it is really small because the previous poster is correct that 2^64 is very small for that purpose - a small supercomputing cluster or two could decrypt such a cipher in a reasonable amount of time, which is why symmetric keys are all 256 bits and up to guarantee there’s no way to attack them.
The only way it would apply to symmetric keys is if you have a server that stores 2^64 encrypted messages, and can somehow find out which messages used the same symmetric key (normally not possible unless they also have the same IV and plaintext), and can somehow coerce the user who uploaded message #1 to decrypt message #2 for you (or vice versa). Obviously that isn't realistic.