I don’t think 4.0 should have that immunity bar, it’s unrealistic and pretty boring.
Instead there should be status effects from consuming bad foods or staying for longer times in contaminated area.
For food poisoning there could be like an status effect icon showing that you are sick. You could have 3 levels of food poisoning: Mild, Moderate and Severe, all with their own status effect picture.
This same thing could apply to radiation sickness.
I don’t know how many more sicknesses and debuffs the game will have but, this could work with any sickness/debuff like infection.
I think this is much more realistic and not to boring like the immunity bar.
(also just a side suggestion, stamina bar could also be removed and replaced with visual and audio effect of breathing and slowing down when running/fighting with melee. Same with oxygen, it would just be a visual effect of darkness closing in on screen and gasping for breath)
All of this would make stuff more realistic while keeping the HUD minimalistic.