That's their total fund and I doubt they are going all in with it in the US. Still, to reach $500bn, they need $125bn every single year. I think they just put down the numbers they want to "see" invested and now they'll be looking for backers. I don't think this is going anywhere really.

This would be a large outlay even for UAE, who would be giving it to a direct competitor in the space: UAE is one of the few countries outside of the US who are in any way serious about AI.