In civil trials there is the principle of “adverse inference”. When the defendant has either destroyed evidence or else has not produced evidence they would have been reasonably expected to have, the jury is instructed to assume they are what the plaintiff characterizes them to be.
I think this principle holds in this case. There is a lot of circumstantial evidence for the Wuhan lab leak theory. The Chinese government has destroyed a lot of evidence and host gone to great lengths to keep documents and people away from investigators.
Based on all this, I think the preponderance of evidence is in favor of it being a lab leak.