So they were creating chimeras from a spike they found that was similar to the pangolin spike but has never been published. And they were combining that with a backbone that they found that was RaTG13-like but similarly has never been published. Even though their prior targets have been SARS-CoV-1 and WIV1 backbones, and they skipped over RaTG13, which would have been of more interest to study because of its association with the miners, to select an RaTG13-like backone of an unpublished virus. And then presumably they did all this in HELA cell lines expressing human ACE2 and did serial passage / gain of function so it became well adapted.
Then even if you have all this happen, you somehow need to get that virus up someone's nose. Because petri dishes don't cough. And we know that SARS-CoV-2 doesn't spread pretty much at all from surfaces. And you need to get a sufficient infectious dose. So someone had a party in the lab and decided to chop up a dish of proto-SARS-CoV-2 cultures and rail a line of it like it was coke or something.
Or, nature does chimeric (recombination) gain of function experiments all the time, and every confined animal farm in China is a bioreactor in a lab doing stochastic serial passage experiments with "lab workers" who have never even heard of biosafety levels.
https://www.biorxiv.org/content/10.1101/2021.01.22.427830v3
https://www.cell.com/cell/pdf/S0092-8674(21)00709-1.pdf
https://www.nytimes.com/2021/06/14/science/covid-lab-leak-fa...
https://www.nytimes.com/2021/06/14/world/asia/china-covid-wu...
At least everyone seems to have stopped yapping about furin cleavage sites this time.