Manganese is a trace mineral your body uses in small amounts to help form bone and connective tissue, support metabolism, and act as part of the antioxidant defence in your cells.
Falling short isn't the concern here. The NIH notes that manganese deficiency is rare, since the amounts needed are small and it's spread across plenty of everyday food: whole grains, nuts, legumes, leafy vegetables, and tea are all good sources.
The number that matters more is the ceiling. Adults need around 2.3 mg a day for men and 1.8 mg for women, and it's best not to exceed 11 mg daily. That limit is really about supplements rather than food, since consistently high intake is associated with neurological effects over time, and normal eating stays well below it.