ISO & Dynamic range - what is going on?

In a camera, the ISO setting normally affects the gain between the sensor output and the raw written data. In some cameras, that gain is fixed and the ISO gain is applied in the conversion software. In the green curve, the gain is proportional to the ISO value; in the other curves, it is not. The blue curve (your Fuji) looks to me like it has "extended" low ISO and high ISO; and the black curve has some trickery in addition to that.

"Extended" means that, for example, that the camera aperture and shutter values are not changed by the ISO setting below "native", say 100 and some high value..

The graphing site owner Bill Claff does respond to questions and can give a much more specific response.

I dont take any of these testing sites (linked to manufacturers 🫣) for real any more, i borrowed a sony a7r5 the other week and put it through some simple tests. it doesnt compare to the a7iv for DR and hi iso performance , just as i had thought, and even worst case is the a6600 compared to the a6700. the a6700 is so far ahead its nearly FF performance based on images i looked at from past cameras with the same sensor, baseing DR on noise is just plain wrong, as a guy said on FM forums how can increasing noise reduction(reducing noise) increases DR 🤔its all a joke. just do your own testing thats the only way you will get the answers.