It looks like there might be a very small effect starting at around 1000ppm but so small that many studies find no difference at all, and reliable effects are only noted at 3000ppm or more.
So we're a long way from needing to scrub co2 from the atmosphere to get any work done
Not everyone in a population will be affected the same by the same conditions, and the constraints of peer reviewed research make them often a poor choice for guiding personal decisions. By the time you have conditions bad enough to statistically prove harm in a large population, you’re likely already way past causing harm worth preventing in some subset of the population.
So we're a long way from needing to scrub co2 from the atmosphere to get any work done