ISO, Native ISO, and exposure range in the highlights & shadows

This is an excellent video explaining these concepts in the context of the Black Magic Pocket Camera 4k.

The same thing should apply to pretty much every other camera out there when recording video.

This is a good video to explain how the dual ISO sensors work. This is what is used by the GH5s and the BMPCC.

As far as the GH5 is concerned you have a standard system for MFT with single circuit

I think people are still confused on why on log iso starts at 400 and normally is 200 and this is due to the compression of the gamma curve