On the US dollar as reserve currency, that is a tough thing to break especially for China since the yuan is not freely convertible. China has renminbi and yuan; one they peg to the dollar and the other is circulated in China. Try converting USD to yuan in Paypal for example? The option is not there. Payments from the west to china sellers by Paypal (for example) are only in dollars.
It is a complex subject since China is the only foreign nation with a direct link into the US Treasury for purchase of US debt instruments, bypassing the Fed’s crooked relationship with its crooked primary dealers. This is done to manage China’s global trade relationships via the value of its currency which is somewhat pegged to the dollar (even if China and Trump claim otherwise) thus evading Federal Reserve gamesmanship. That’s why Trump messing with China is so dangerous, even if China has few options right now.
As a result of this ‘trade war’ China has let the yuan slide versus the USD which is a warning to Trump, specifically Mnuchin, popularly known as one of the most slippery dealers (IndyMAC and One West) to ever walk the earth (and China knows that). China is hoping that a lower yuan will offset tariffs just as the US has ‘weaponized’ the dollar and has imposed sanctions and tariffs on China. Because the sums are so vast with China holding so much US debt, and because China depends on exports to the west, China is somewhat boxed in.