Basically, instead of the bar being fully solid when the linked item (i.e. a storage or timer) has reached its max, it instead will be fully empty. So, for an empty storage linked to a progress bar, the bar will be completely solid, and so on. Usage case: cooldown indicators.
Allow inversion for certain ProgressBars
Should already work, set Invert = true on the ProgressBar component.
I usually do after exploring all alternatives and come up with better than a simple solution which sometimes comes months or year later or not at all 