@ariadne The most shocking part of your post is that you consider 2019 an old paper!
I am dubious about cloud models and climate models with clouds. But I think the important take-home of this article is that there are plausible physics which suggests stratocumulus can disappear, rather than the CO2 concentration at which it would happen. And the uncertainty of the concentration level coupled with the physics of cloud formation stopping should be more pressing to us. What if the practical limit is 500 ppm rather than 1200? Is society preparing for that?