There is a maxim in science:
the absence of evidence does not prove the evidence of absence.
That means because there is no evidence to prove one theory, it does not prove that that theory is incorrect.
Obviously the same argument is used extensively by God believers, and other conspiracy theorists.
Because no evidence has been found to prove the theory that the Covid virus was produced (and escaped from) a lab in China, it does not disprove the theory.
However, the same argument could be applied to any such theory, e.g. the US invented it and planted it in China, it arrived on a meteorite from outer space, etc.
The subtle difference is that the theory that the virus was manufactured in a Chinese lab, and escaped from that lab is only the dominant theory in western circles, possibly given greater prominence by Trumpists.