Dark Material
It interacts only through gravity and has no electromagnetic interaction. Naturally, since its interactions haven't been confirmed, there are various hypotheses. First, some suggest that dark matter might interact like ordinary matter and could form planets like Earth, leading to humorous claims that dark matter might be ghosts. Personally, I propose explaining dark matter as curved space itself - suggesting that it's space that has become "loose" or "worn out" due to existing gravitational forces, which would explain why it doesn't interact as a conventional substance.
Dark Matter Notion