The optimal CO2 level isn’t even constant between plants, but at the upper end “good for plants” is the same as “makes humans 25% worse in memory speed/accuracy tests”.
Humans have high adaptability to increased CO₂ loads (see e.g. freedivers), but adaptation takes time. The studies usually deal with temporary CO₂ increases / O₂ decreases, often in way higher concentrations like 1-10%, whereas a couple percent atmospheric CO₂ would already burn us to a crisp (figuratively).
https://escholarship.org/content/qt6gm6t5zc/qt6gm6t5zc.pdf?t...
Seems there is merit for concern, though I stand by my claims of cognitive effects probably being more temporary than permanent.
[1] https://www.lesswrong.com/posts/DtQzYXBTwaWXbhCoS/stale-air-...
[2] https://www.advancedsciencenews.com/co2-on-the-brain-and-the...