Special Drawing Rights (SDR's) magically appeared but you're right, a government or multi governments currently need to back the Global reserve currency. Unfortunately, the US has a habit of sanctioning countries and denying them access to the global monetary system, in effect weaponising the US dollar. This imho will be the downfall of the USD as the reserve currency. Only takes Russia and a lot of OPEC friends to go with China's digital currency to purchase Oil and a lot of other people will follow. Maybe not the G-7 but possibly the rest of the world. If it isn't Chinas digital currency, maybe it will be the IMF or world bank or the WEF.