The Chinese yuan is not a viable reserve currency. Why? Because it's pegged to a basket of other currencies. It should really inflate in value but Chinese government policy is to undervalue it to aid exports. Exports are ~20% of China's economy. It would devastate the economy if the yuan was allowed to freely float, or at least float with the level of central bank management that other developed nations' fiat currencies have.

China has repeatedly tried to activate a consumption economy (like the US) but the Chinese just save and buy real estate, in part because there is no retirement benefits so they have to self-fund that.

So what currency? Currently, there is no viable alternative to the US dollar. It is backed by the largest economy in the world AND the US military.

You might find people who talk about BRICS like it's a real thing. It is not. It's just a group of randomly selected countries meant to sound nice (literally, South Africa is only there for the S sound) with no unified policy or currency.

It's not the euro either. Europe ultimately is still dependent on US defence and beholden to US foreign policy.