That's why the Party is so dangerous, absolute power.
The US government says something, US businesses say no all the time, and policies are rarely thoroughly enforced. Also, if the Congress or WH switches hands, policies are often adjusted or rolled back.
When the Party says something, nobody in China dares say no, and the supreme ruler now rules for life. If COMAC were to obtain the capability of manufacturing large passenger planes, and the Party would be free to ban Boeing, then not a single airline in China will buy Boeing, and you certainly won't be hearing news like "Companies still want to buy Boeing because Boeing has better fuel efficiency" etc. The next day France voices support for democracy, or something else that rubs the Party the wrong way, and no Chinese airline will buy Airbus. Same goes for any country, any business. China is the world's largest single market by far, and a Chinese ban would be far more damaging than a US ban, just ask the world's largest car manufacturers for example, which will get them bankrupt faster, a US ban or a Chinese ban.
People of the world, deal with the Party while you still have the chance.