I recommend "Broken Dream Immortal Destiny" and "My Phone Has Miracles" to you. The former was a story about a cultivation world where the protagonist could kill people in his dreams, while the latter was a story about a modern city where the protagonist had the ability to control dreams. The protagonists of these two novels can control their own dreams, which is very suitable for your needs. I hope you will like my recommendation. Muah ~
One consequence could be that the wizarding world starts to view him with even more suspicion and fear. People are already afraid of dementors, and if Harry can control them, they might think he's becoming too powerful or even turning to the dark side.