Calculate the probability then. With 64 bits 2^32 tries have a possibility of ~0.39347 collisions. Which is unlikely, not likely.
You need at least 10x more to get a good probability of %97.
Which needs ~40m with 8 cores on my CPU. Which is not a practical flyby attack anymore. With a big GPU it would though.
I do calculate 32bit collisions for all hash functions regularly. But not for 64bit functions, because they are not practical. Google is the only prominent one who cares for 128bit, but then they should at least get their numbers right. Because most of their arguments are pure security theater.
2^32 is 2 months of 1000 random requests per second, so every 2 months you'd have a random chance that your service breaks for someone if you're relying on there not being any collisions.
https://kevingal.com/apps/collision.html
I do calculate 32bit collisions for all hash functions regularly. But not for 64bit functions, because they are not practical. Google is the only prominent one who cares for 128bit, but then they should at least get their numbers right. Because most of their arguments are pure security theater.