There are not a lot that other countries could do about Hong Kong or Xinjiang. Pretty much limited to diplomatic and economic pressures.
Taiwan is more straight forward. US and other western countries just need to make it clear that they will defend Taiwan. Not a hard decision to make. The world semiconductor market is dependent on Taiwan. It is one of two countries that produced 5-nanometer silicon wafers, and the only one producing 3-nanometer silicon wafers with 2-nanometer wafers coming soon. We can’t let China get their hands on Taiwan.
Somebody mentioned that only 7% of the chips manufactured in China is used domestically. The reason for that is that China can’t make the high end chips that it needs. Currently it can only make 14-nanometer silicon wafers. It has failed several times to build fabs that can make 7-nanometer wafers. Here is a good reading - Semiconductor fraud in China highlights lack of accountability. So for its technological development, China is dependent on the US, South Korea and Taiwan.
US has a lot of leverage when it comes to using high end chips to limit or slow down China’s technological development. All the high end chips manufactured in South Korea and Taiwan use US licensed technology. If the US say “don’t sell to China”, they won’t sell to China. In fact, currently they need a special US license to sell to Huawei.
US also has almost 100% monopoly on the tools needed to manufactured those chips which turned out to be even harder to manufacture than the chips themselves. The world’s most important suppliers of these tools needed to make high end chips - Applied Materials Inc. (Santa Clara, CA), KLA-Tencor Corp. (San Diego, CA) and Lam Research Corp. (Freemont, CA) - all hail from the US. You can’t build a fabrication plant or even perform research without their tools.