There was a nucleotide sequence in the covid strain that did not show up in any of the proposed hosts or progenitor viral sequences, which is where leaked documents showed NIH (Fauci included I believe) discussing the non-natural origin of the nucleotide sequence. It's possible to search for articles about the Fauci NIH emails, and whether they mean anything scandalous.
Here's a technical article at NIH discussing the theory of no known natural origin for a nucleotide subsequence
This is an open access journal by two people whose publication history you can look up if you want to draw your own conclusions. Read the disclaimer at the top of the link. Don’t bootstrap its credibility by linking it to being at NIH (which does mean something) anymore than saying something found on Google is from the company itself.
Don’t imagine any bootstrapping of credibility is stated. It’s a citation to one article of many with no assertion otherwise. That’s how science discussions work.
Here's a technical article at NIH discussing the theory of no known natural origin for a nucleotide subsequence
https://pmc.ncbi.nlm.nih.gov/articles/PMC8209872/