You might have scalp psoriasis. I always thought I just had bad dandruff and tried shampoo and leave in treatments and they didn’t really work. I got it checked and it’s actually just psoriasis (plus regular dandruff too, but the dandruff was exponentially worse because of my psoriasis). You could maybe get a dermatologist to prescribe a topical steroid. It helped for my case (you might still need a dandruff shampoo to go along with it)