Waxy spot in hair with dandruff (or maybe just sebum?) even right after washing... how can I get rid of this?

Some more info:

My hair is super long (past my butt) and very fine. Used to have a lot of it but it's thinning out, particularly in this problem spot (front of head), it seems.

I wash about every 3-4 days. My hair has this gross spot even immediately after washing. I stopped using sulfates a while ago. I do use Lush's dry shampoo regularly, particularly on this spot since it's always so gross... maybe it's making it worse? I use Live Clean shampoo/conditioner and have for years, never caused a problem but maybe something changed?

I can't pinpoint when the spot came up, maybe, a year ago? Maybe longer? But this exact spot on my scalp seems to almost always be waxy and filled with these white specks, I'm not sure if it's dandruff since some of it is hard. It does get itchy sometimes. There's also lots of sebum build-up in that spot.

How can I get rid of this spot? It's disgusting and making me super self-conscious. :(