Although you can find a Bayesian answer for this which I am not qualified to calculate, it's irrelevant. The most pressing issue is not to dismiss it as zero probability as has been until know because it is viewed as a conspiracy. Even if the probability is very small we have to dig in deeper to prevent the next catastrophe.
Can we prevent a volcano erupting? No. Can we prevent a lab leak? Yes. I wonder why people are soooo resistant to this idea and make up a myriad bad arguments.
https://en.wikipedia.org/wiki/List_of_laboratory_biosecurity...
SARS itself leaked from the lab 4 times, once from a BSL-4 lab.