Quantum computing. It might be a real thing but it’ll go through a grift phase first.

Another one will be environmental carbon capture, like pulling carbon out of the atmosphere. This one would be easier to fake but might not get traction for longer since the ideological superstructure in our society is already built up so that it is hard for a political crisis to emerge due to global climate concerns. Even though climate change is worsening, and whole cities are being destroyed by hurricanes, the debate is still pretty stabilized. However since this grift will end up being sold as a commercial solution to a political problem, the grift will probably come from a larger player like Lockheed or Boeing, which would necessitate investing in the most evil companies in existence. Still you never know, Tesla stayed afloat for years without making a working product by selling carbon credits issued by the government to other car companies, so you might be able to bootstrap this one