I already referenced the Green Sahara cycle, I'm aware. The green period only lasts ≈10,000 years per cycle. The entire cycle is ≈23,000 years, and is tied to the Earth's axis wobble. It would be far more likely to find evidence in a more stable area rather than somewhere that causes Lake Chad to become Lake Gigachad (not what it's called, I know, don't care, sounds better.) every ≈13,000 years. There's a fuckton of water moving through that area from what we can tell.

I also have lived on, and grew up on a farm, in the Midwest, tons of arrowheads of you knew where to look. The thing is that archaologists would literally kill each other to find any evidence of modern agriculture that is older than 12,000-15,000 years ago. They've found plenty of stuff to indicate that we spread out well before then, and that there were hunter-gatherer civilisations well before then. Not one of them has yet to find any evidence, even with the latest scanning tech that allows us not to dig, that anyone was farming prior to 12,000-15,000 years ago, and then we all started doing it. If archaologists can find evidence of something humanoid (may not have been homo-sapiens) in the area of San Diego either 125,000 or 250,000, I don't remember, years ago way back in the '90s, and they haven't found one shred of evidence that farming existed prior to 15,000 years ago, I'm gonna have to go with the professionals here.

We've found evidence of ancient cultures that existed in the Green Sahara, and in South America. They've flown ground penetrating scanners over almost all of the planet at this point. Someone would have found the data.