Comment by rimliu

"Dual native ISO" sensors don't perform different amplification before the read out amplifier or anything like that.

With an image sensor you get to decide between high sensitivity and high capacity (how much light it can detect before saturating). So a highly sensitive sensor can handle less light before clipping (which makes sense).

This trade-off can be tweaked by changing the size of the photodiode (bigger diode -> more sensitive), but also electrically - simply add capacitance in parallel to the photodiode. This requires more energy, i.e. more photons, to change the voltage over the photodiode, which is what the readout measures.

Dual native ISO sensors simply add another transistor (as a switch) in series to extra capacitance; this allows them to switch between low-capacitance (high sensitivity, but saturates faster) and high-capacitance (lower sensitivity, can handle more light).

Edit: Haven't watched the whole video but his core explanation in there seems to be that Dual ISO means the sensors has a PGA (programmable gain amplifier) -- almost all sensors use that approach, and that's what is controlled by the ISO setting in them.