When my ferritin was 11 (so within range and not flagged!), my doctor prescribed ferrous fumarate tablets, taken every second day. Research shows slightly better absorption when taken every other day, because of liver binding globulin or something, plus it’s easier to manage when you don’t have to take it every single day (with vitamin C, away from dairy, caffeine, and other medications).
I’m a blood donor and I have restless legs syndrome so I ask for my ferritin to be checked when getting any blood work. The highest I’ve seen it for me is 45.