You don't have to go back that far. It's fluctuated back and forth between 160 to 300ppm over the last 800k years. https://science.nasa.gov/resource/graphic-the-relentless-ris...
Just popped up on my news feed, "Archaeologist braves the Joe Rogan podcast to counter Graham Hancock's nonsense":
* https://boingboing.net/2024/04/19/archaeologist-braves-the-j...
Episode in question, "Joe Rogan Experience #2136 - Graham Hancock & Flint Dibble":
* https://www.youtube.com/watch?v=-DL1_EMIw6w
(Entire episode is 4h26m long: I don't have to interest/patience for that personally.)
You can watch 70 minutes of another youtuber reviewing the debate:
Just kidding. I suspect that's an interglacial when you have warming and melting but before the trees have grown back to recapture the co2. But check with an expert if you want a more authoritative answer.