I have no idea, but I know for a fact that the AK620 it's slightly better than the other Noctua killer, the Thermalright Peerless Assassin 120 SE. The Thermalright PA 120 is cheaper than the AK620 and I would have totally bought it but there is no distribution and warranty service in my country so I opted for the slightly more expensive, but also better AK620.
If you're interested in Thermalright coolers, I would suggest going for the PA 120 SE, it's cheap, has more heatpipes and it is more recent than the FC140.
edit: Forgot to respond to your other question:
The black version is called ZERO DARK
It's a bit more scarce, because it was released last autumn. But a big bonus is that it contains LGA1700 mounting kit, unlike the 2021 non-black version.
I'm guessing that now that the Chinese New Year is over, these should be restocked soon. Just a guess. There is plenty of Zero Dark inventory in my country, strange that US is out of stock.