bell-cot is simplifying but is basically describing correspondent banking. Banks in other countries need correspondent banking relationships with US banks in order to work with dollars. Banks in countries on the OFAC list can't get these relationships. Even banks in "high risk" areas like the Caribbean are getting their correspondent relationships cut off because US banks are worried about getting fined if the banks they correspond with doesn't have strict AML procedures. See https://www.atlanticcouncil.org/wp-content/uploads/2022/02/F...