One issue is data exchange. Many computers exchange data, certainly in international banking. If one computer on a network is not ready, it might corrupt the data in the other computers that are ready. If trade is disrupted, medicines may be in short supply. Much of the petroleum comes from countries that are far behind in their y2k programs.
International trade requires international phone calls, banking transactions, and shipping.
Shipping is one sector that is far behind. Ports tend to be quite automated, at least major international ports. In Turkey many people rely on the fact that the level of automation is not that high and that people are anyway used to disruptions. Most of them do not know about the problems of the natural gas suppliers in Russia, where we take our gas from. Yes, many people in less developed countries think they will not be greatly affected since they use fewer computers.