My husband uses Minoxidil like the other commenter mentioned, it works for him but I personally haven't tried it. Make sure you're getting enough protein & vitamins through your diet. I take Collagen in my coffee every day. I tried Biotin but I prefer Hers or Nutrafol for noticeable results, if your budget allows. I'm also trying out the Multi-Peptide Serum for Hair Density by The Ordinary to make it appear fuller in the meantime. Olaplex shampoo/conditioner no more than once a week for me, I do regular hair wash in between. Hope you find something that helps! I went to the doctor to rule out vitamin deficiencies, hormone imbalances, etc multiple times because I'm at almost 2 years PP and still dealing with this but I also breastfed for a long time.
Nutrafol the postpartum one and then I use OUAI scalp serum every night
Minoxidil