Nuclear missiles require warhead miniaturization

Is Foxo's nuclear missile program close to threatening the other players?

No. The weapons remain years away, and fitting nuclear warheads to missiles requires a separate miniaturization project.

A nuclear bomb and a missile capable of carrying it are separate development goals in Hearts of Iron IV. The estimates put viable nuclear missiles and thermonuclear weapons several years away. Warhead miniaturization is an additional special project required before nuclear weapons can be fitted to missiles. The different estimates reflect the players' plans without establishing an exact completion date.