they have the tech to make some. the issue is to make computers as powerful as they are today you have to make the chips smaller. China, and most of the world, has the tech to make them to a certain size, but not smaller. There are a number of nations who can make smaller than what China can, but Taiwan and either the Netherlands or Belgium, are the only ones who can make the best.
The European country was the one who invented the tech for the current best semiconductors, but they didn't have the manufacturing for it. Taiwan did. They only gave them the tech in a limited way to keep the IP from falling into the wrong hands. Whichever European country created the tech is ramping up their manufacturing, but they have a long way to go. That's why Taiwan makes 90% of the best as quoted elsewhere.
The US has been trying to get the tech too, our military, but the european country is refusing to sell. so we are now actually paying them/giving tax breaks or something, as long as they are able to maintain the stranglehold on the tech, and also don't sell it to anyone else. so if we can't buy it, we are making sure no one else can buy the tech to make it. The chips themselves we don't have that policy of, just the manufacturing. Although I have read we are back dooring the actual chips themselves too. My understanding is we are offering above asking price for far more chips than they can produce. Basically we are trying to strangle the ensure they only sell to us. This hasn't been 100% effective, but my understanding is that we are getting more of the chips than we otherwise would. I think we were even asking straight up how many do we have to buy for you to make this in America, and we will pay it. and I was hearing some stupid numbers, starting with a "T"
I very much doubt any Taiwanese citizen has access to anything important enough to recreate the tech in China.
this is part of the reason the Chinese are looking into quantum computing so much, as that helps "reset" the miniaturization issue. you still need powerful semiconductors, but you can make it work with what the Chinese have.
The US is still a leader in researching and designing semiconductors but like everything we else we opt to let an Asian country produce them to save a buck. It would take time to get the infrastructure in place, has already started, but we are more than capable of producing the best semiconductors available. We are definitely not behind in the technology.