There are two meanings for this.
1. Someone whose gender identity is influenced by their own dreams.
2. Someone whose gender identity is influenced by Dream, the Youtuber. Associated pronouns are Dre/am.
The first definition is valid, while the second is not. Dream is a very morally bad person, being a literal pedophile and groomer. However, the first is just about dreams. An example of how dreams may affect your gender is if your gender identity changes in your dreams, whether it is different in every dream or is the same in every dream, but differs from your gender identity outside of dreams.
Person A: Iâm dreamgender!
Person B: In the sense of your gender being influenced by your own dreams, or the youtuber Dream? Get away from me if itâs the youtuber.