What part of it do you doubt? It’s obvious that clouds are white, and it’s obvious that they are cooler than the earth and even colder higher up (clouds form because the adiabatic expansion of rising air cools it down and causes water to condense, and the higher up you go the colder the atmosphere due to greater expansion - anybody who has hiked the mountains has experienced this).

The only assertion here that one has to take on faith is that clouds are approximate black bodies at infrared wavelengths (which isn’t surprising - most things tend to be), and the relative magnitude of the cooling vs warming effects. Oh and there is an unstated dependency that the Earth is also an approximate black body at infrared wavelengths.

I think the concept of the albedo of the poles is another simple idea that explains why melting poles would be bad and accelerate global warming further, because by being white they reflect back sunlight for a huge area. Kinda intuitive if you have ever touched the black (opposite color) coolers on a desktop computer and felt your hand fry

Granting that the two effects counteract each other, it is surprising that the crossover point would happen within the range of variation of actual clouds on Earth. My uninformed guess would have been that nearly all clouds' effects are dominated by only one of the two effects—probably, by the cooling effect.