What you really meant to say is, "where is my evidence", and well we've been doing this since 2012, at least.
If you don't want to be banned, you're welcome to email hn@ycombinator.com and give us reason to believe that you'll follow the rules in the future. They're here: https://news.ycombinator.com/newsguidelines.html.
On the other hand if you have not read the DEFUSE proposal you are in for a real treat. It is absolutely plausible that sars-cov2 could be an output of this line of research.
We also don't really know what backbones they had.
But if we're looking at specific claims about applied research apparently featured in the book: that it was [most] plausible details like the spike binding to ACE2 receptors were the product of human ingenuity applied to RATG13, the likelihood of this seems to have been undermined by the subsequent discovery of other naturally occurring viruses more similar to SARS-COV-2 already featuring a spike capable of binding to human ACE2 receptors.
Ultimately I guess the question is whether the intermediate viruses between SARS-COV-2 and other variants are more likely to exist in secret in the labs or outside the scope of human knowledge, I guess. I do believe it is possible for virologists to cover up things in their lab especially in this context, but outside the scope of human knowledge is a bigger search space.