Saudi Arabic collected USD from sale of crude/oil and purchase bond in USD issued by Tiongkok
in return get to invest in their country infrastructure for HSR, high-tech industrial park, building factory, financial system, ...
Tiongkok can lend the USD to Global South countries in need of it to pay off their debt to EU or US preventing any default and their assets being sell cheaper to the lender
Over the time, Beekok will be flooded with their own accumulated printed fiat currency, it will cause serious high inflation
There is nothing much Beekok can do(in the past BK just start a war with them but not presently) except to issue warning to those countries that are dealing with Tiongkok to stop