These foreign investments are mostly not currency. When a foreign country makes a lot of investments in the US, they could be buying stocks, bonds, or making di

These foreign investments are mostly not currency. When a foreign country makes a lot of investments in the US, they could be buying stocks, bonds, or making direct investments - such as building US factories, as many foreign auto makers have done. Or buying entire companies - one of the big three US auto makers (Stellantis) is now foreign-owned. Stable countries that have a lot of attractive investments will tend to have a large trade deficit, and the US is one of the more profitable places to invest. (Well, not so much at the moment.)