Collisional broadening - which includes van der Waals and Stark broadening - is more important in the higher gravity, higher pressure/density atmospheres of dwarf stars (a factor of 100-1000 higher for dwarfs vs giants of the same photospheric temperature).
These collisional effects effectively "truncate" radiative emission and absorption processes,...
Radiative energy transport continues. The point is that the radiative flux, which is proportional to $dT/dr$ can be overtaken when the temperature gradient achieves the adiabatic value and convection starts. Once convection is started, it is very efficient and the majority of energy flux will be transported by convection.
Broadly speaking, radiative ...
If you go back to the sourced article in your graphics by Jennifer Johnson it has a more verbose colour legend. For the grey part it explicitly states
very radioactive elements. Nothing left from stars.
and her figure caption more verbosely
Each element in this periodic table is color-coded by the relative
contribution of nucleosynthesis sources, scaled ...