FWiW you appear to basing your take on a reading pushed by Dr. C.A. de Lange of CO2Coalition of an unaccepted paper by William. A. van Wijngaarden and William Happer.
That discussion on Stackexchange has something like 6 upvotes. And if you read it, the comments there are mostly ridiculous. The absorption is logarithmic beyond 8000 ppm, and someone there e.g. whines about that Wijngaarden doesn't explain the climate on Venus (> 90% CO2 atmosphere).
The thing about Venus is also something you'll find if you look for serious papers trying to criticise the paper. Nitpicking about the word logarithmic seems to be the only things that serious critics have found. The other main argument seems to be name calling and Cancel Culture... and that's all what critics so far have produced...
Claiming that things are unaccepted is also some kind of rumour. There are more papers, and if you read them you'll notice that they're of very high quality. Just compare the quality with that of papers of critics...
To me the most compelling argument for Wijngaarden is the incredible low quality of all the writings from people from climate-institutes that tried to find something against him. OMG...
Original paper (on arvix, not accepted by any mainstream journal so far): https://arxiv.org/pdf/2006.03098.pdf
C.A. de Lange loves it, claims it as game changing etc: https://co2coalition.org/publications/van-wijngaarden-and-ha...
There are a number of discussions re: the original paper and why it was not accepted, eg:
What is technically wrong with Wijngaarden & Happer's paper claiming to show that CO2's contribution to surface warming is saturated? - https://earthscience.stackexchange.com/questions/25227/what-...