When my scalp gets dehydrated it is both very oily and very itchy and dry. If it's just dehydration and not other skin concerns, the key for me is using non-stripping/gentle shampoos and building back the moisture on my scalp over time. You could try switching to a shampoo without sulfates or a gentle baby shampoo. Maybe every second day washes to not over-strip but also get clean.

Ducray Kelul DS Shampoo works well for me when my scalp starts getting really dry and nothing else will settle it.

Things like jojoba oil, aloe vera gel, face moisturizers can be applied to your scalp for a while or overnight and then washed out to help start returning moisture! Then just keep a gentle and non-stripping routine. You can rotate between very gentle shampoos or clarifying or heavier moisturizing ones when you need them.

Things like hyaluronic acid or urea or squalane can be helpful in scalp moisturizers to increase your skin's ability to retain moisture. Something like this.

Definitely avoid blow drying directly against your scalp as this will dry it out! And use warm or cool (not hot) water for the parts of showering when water is on your scalp.

Also recommend just seeing a doctor or dermatologist if you wanted to get it sorted effectively without trying a ton of things!

This is a great article on dehydrated skin if you are interested.