These debts are counted and traded in US dollars, which are foreign exchange from China's exports surplus. China has trillions of dollars in reserves. Considering dollars' credit loss, China intends to spend them rather than let them shrink in pockets. If 3rd-world countries can repay their debts, that would be the best. If they can't, then use ports, mines, etc. to exchange. If that still fails, China will pay its companies/workers in CNY, while successfully spreading China's tech, infra, standards & culture to these countries. China is still winning.
Remember: China is using US' money to make loans & expand its influence (helping developing countries with tech & infra). China is not losing even in the worst case. Given China's massive surplus every year, it has to be spent in some way. This is BRI's genius point. China is shaking the US empire from the very root.
