My brindle Nyala gets that on her butt area like yours. I donāt wash her too much either so she can keep her natural oils. Up his meals with wild caught frozen fish or add a can of sardines to his meals once a week. But do brush that area more. Nyala has a thicker coat like yours on her butt n needs to be brushed out. You can also add coconut oil n massage in.
Yes, that looks like dandruff.
Bathing too often can cause dry skin.
Coconut oil can help. We use a squirt bottle (like a restaurant ketchup bottle)and heat it up in the microwave 'til in a liquid state and squirt a circle right on top of AM kibble.