Would entirely change China’s history. If Qing emperors weren’t so close minded and xenophobic and actually opened up their country to trade circa 1700s, everything would change.
First of all, China would be the first to industrialize in Asia, not Japan. If Japan did not industrialize first, it would have lost to China and the Sino-Japanese Wars (both of them) would end up with Japan being defeated. The Opium wars similarly might not have ended up as lopsided as it did. Same for Boxer Rebellion. If the late Qing emperors (after Qianlong) were actually competent (let’s not forget Dowager Cixi made some crucial mistakes as well), China’s Qing dynasty might have lasted another 100 years.
China would not have lost Hong Kong to the British. They would have not have lost Taiwan to Japan. Korea would likely still have been taken over by Japan but it’s possibly Japan would not have taken over Manchuria because Qing would have defended that.
If Qing held on to their territories and defended themselves well and had competent emperors, Xinhai revolution would not have happened and ROC would not exist which also means PRC would not exist. If Qing lasts another 100 years, your guess is as good as mine because I have no idea honestly what would have happened there. It’s probable that Japan would not have become as powerful as it was, the Japanese Empire would be weakened, China would have been stronger, and perhaps that would have led to a Cold War era with three superpowers: USA, USSR and China. Likely China would end up closer to something like Russia’s government today? Which ironically, is not too different from what China is now. (but China would have avoided the Mao-era with the famines / cultural revolution)