Can I apply for a DARPA grant, being a foreign citizen who has founded a company in the US?
The company would be located in the US and there would be other founders with US citizenship.
The issue with FOCI might be on sensitive projects. But there is nothing that I could see that you can't apply for the grant and be awarded it if you are a foreign citizen or a company.
P.S. Of course I don't know if you are in one of the no-trade countries in which case ...
Virtually every public company in the US has foreign investors. That by itself does not preclude a company from getting a DARPA grant.
An example of a DARPA grant given to a company with foreign investors is the Boeing X-37 project.
Boeing is a publicly traded company with foreign investors.