So with ZK-proofs we may never be 100% sure something is true or not? Is it possible that this may be too computational expensive to have certainty at given (or above) level?

You don't necessary get 100% certainty but the probability of success increases exponentially with each new run.

Thus you can get very fast to a probability smaller than you quantum tunnelling through a wall

Yea it's the same as a hash collision, maybe they managed to type some other message that hashes to the same thing but it's very unlikely.

You can also use multiple different types of ZK proofs for the same data, same as using multiple hashing algorithms, for more certainty.

> we may never be 100% sure

Right, but we may be 99.9999999999% sure.

It’s the same thing as regular cryptography, I can’t be 100% sure that you signed this message but I can get arbitrarily close, and prohibitively expensive to fake

That's very cool! Here's another cool application for nuclear arms control, https://www.nature.com/articles/nature13457