I can only find sources saying that the Furin cleavage site doesn’t rule out engineering, or sources saying the Furin cleave site could be naturally occurring. Sounds like we don’t know yet.
https://nicholaswade.medium.com/origin-of-covid-following-th...
As addition of a Furin cleavage site is an old hat acknowledged technique for increasing human infectivity of a virus. The issue with a zoonotic origin though, is that the odds of a mutation is incredibly small, and a recombination at that site would require the sequence to exist in another coronavirus, which has not been discovered to date.
It is also known WIV researchers had recieved instruction from another virologist on "no-see-um" editing techniques that would not leave traces of the mechanism used to splice in an edit.
So not proof, but the network of coincidence is as hard to ignore as a spinal tap amp duct taped to your head, cranked to 11, playing the 1812 Overture.
https://twitter.com/wanderer_jasnah/status/13942477140246609...
Some more reading: https://www.news-medical.net/news/20210217/The-origin-of-SAR...
All these lines of evidence and reasoning show that the acquisition of the polybasic furin cleavage site by SARS-CoV-2 is a “missing link” in our understanding of its evolutionary history, that can only be addressed through the discovery of new viruses.”