So much of the coronavirus origins debate seems to thrive on a deliberate conflation of engineered bioweapon and accidental lab leak of a natural virus.
Documents from the House Subcommittee on the Coronavirus Pandemic share the peer-review process for the Proximal Origins paper. In discussions with the reviewers, the authors make clear to note this distinction. The Proximal Origins paper shows why SARS-COV-2 is not an engineered bioweapon, but offers three theories for its origin, two that are zoonotic spillover, and one that is a lab leak of a natural virus during passage in cell culture.
In the peer-review, one reviewer dismissed the lab leak theory, but the authors were quick to note that it can't be entirely ruled out. I've seen people argue the Proximal Origins authors had an agenda to cover up a lab leak, but here you can see quite the opposite. They were considering all theories and following the evidence. They thought zoonotic spillover rather than lab leak was the most likely scenario and laid out the reasons they thought that in the paper.
https://www.nature.com/articles/s41591-020-0820-9
Here's the original Proximal Origins paper. It holds up well still for laying out the evidence inherent in the virus itself. Most of the evidence really hasn't changed since then other than some more circumstantial evidence to support zoonotic spillover.
The three theories are listed in the paper. What is dismissed is the engineered bioweapon theory as evidence in the virus itself undermines that theory.
As the paper notes, there are some reasons to think cell passage is unlikely. Notably features of the virus that seem to indicate interaction with an immune system. But also the lack of a known progenitor virus in lab specimens (the Wuhan Institute of Virology did publicly disclose viruses it sampled). And features of the virus found in other viruses in nature.
We also have some indication that rather than generating a furin cleavage site, repeated passage generally would get rid of such a site in this case.
And since the paper was published we have some more evidence that generally undermines a lab leak theory. Two distinct lineages of SARS-COV-2 emerged early on in the pandemic and analysis seems to indicate these were from two separate introductions. This would generally point towards zoonotic spillover, rather than a lab leak.