Those are noise power density graphs that show that signal went through a low-pass filter. On Sony cameras without 'star-eater' and cameras from other manufacturers it is flat.

But I admit that this issue is most noticeable on S-series (low resolution/high sensitivity) cameras, as their lower resolution makes it easier to resolve stars down to 3x3 pixel size. Normal and R-series cameras have such high resolution that it is hard to notice and not much of a problem in amateur astrophotography.

I have not seen any proper tests of latest A7S III as it was only released last month.