It's true that high CO₂ levels cause cognitive impairment, but submarines routinely operate for months in the 2000–5000 ppm range, sometimes as high as 13000 ppm, over 30 times higher than the current atmospheric level but still too low to kill people by about a factor of 8. Subtle cognitive impairments at these levels have been found by some researchers, while others have been unable to replicate them even at 30000 ppm: https://pubmed.ncbi.nlm.nih.gov/29789085/ https://www.nap.edu/read/11170/chapter/5#54

That's why the NOAEL is set at 25000 ppm, at which point CO₂ starts to cause visual disturbances, which I think fall short of "toxicity"; it's more like a recreational drug effect. If the Earth's atmosphere reached 100 times the current level, 40000 ppm CO₂ (4%!), you still wouldn't have a CO₂ toxicity problem in humans. However, you probably wouldn't have a biosphere much longer either, and at that point toxicity to humans would be a moot point.

Also, by the way, the quality of the discussion would probably be significantly improved without you saying, "You obviously have no idea what you are talking about." Sometimes people might disagree with you because they know things you don't, for example because their information doesn't come from science popularizers, rather than because they don't know things you do. If you don't keep that in mind, you are likely to embarrass yourself frequently. Believe me, I have a lot of experience doing that.

Less sneering, please.