There's no need to block chip imports completely.
The Chinese government can mandate the use of Chinese chips, even if they are more expensive or perform worse.
After some time, Chinese chips will be competitive.
Of course, the US also has a say in what chips China can import.
Nothing is irreplaceable. Even if the Russians banned the export of engines, the United States banned the export of electronic components, Germany banned the export of CNC machines. China is capable of making similar machines and equipment, not better than imported goods, but it is good enough to use and the quality may improve over time.