The PRRAR FCS not a known FCS prior to the pandemic so it is unlikely the lab would have genetically engineered it and they would have used something like RRXRR instead.
Other coronaviruses have an FCS and they have evolved multiple different times, independently:
https://www.sciencedirect.com/science/article/pii/S187350612...
The fact that we knew that adding an FCS to a virus would likely enhance its ability to produce a pandemic really isn't a smoking gun that we actually did it, because we're just studying and copying what nature is already doing (who is actually a much better geneticist than we are, with vastly greater tools).
And since you want to talk about suspicious "unicorns" how about the idea that a lab worker was infected in the lab, and then the only thing that they did was visit the wet market. They didn't infect anyone they lived with, or go to any restaurants, or go visit grandma and this Typhoid Mary/Mike has no existence outside of working in the lab and visiting the wet market. And this idea gets worse if you include more workers in WIV having supposedly been exposed.
What fits with the facts better is that they genetically engineered the virus in perfect secrecy and deliberately let it loose in the wet market, which is just insanity--nobody gains anything from doing that, but it is also impossible to argue against.