You can exclude tags by going to your Store Settings page and scrolling down to “Tags to Exclude.” You can only exclude up to 10, and this only works for games that are actually tagged with the word. It doesn’t exclude keywords in the description. I don’t know how many games are actually tagged with “dystopian.” I get 3195 results when I search for the “Dystopian” tag, so at least you can exclude those.

This works best for genre types.