I attend a lot of graduations (academic) and dress appropriately - dress with jacket, or suit. And smart shoes. It’s an important formal occasion in my students’ lives, so I want to respect that. If you use that thought as a guide, then maybe that helps?
Jeans and T-shirts would look out of place in my mind, because culturally and historically humans do tend to dress up for important ceremonies - it’s a way of marking the specialness of the occasion - it’s an out of the ordinary moment.
Hats are not good, as you obscure other people’s views, but a more than everyday dress, a suit, - basically, think smart clothing that shows your pride in your DC and you can’t go wrong.
have a great day - I always love seeing my students dressed up with their proud parents!