> Suppose tomorrow it was announced that China has brokered a peace deal between Ukraine and Russia and that they will send peacekeepers to ensure compliance.
I literally do not think China has the international clout to make that happen. China is deep in kahoots with Russia, and any deal brokered by them is no more likely to hold than the previous treaties. Ukraine's ultimate goal is to have the same security that other NATO countries enjoy, and that's not something China has the authority to offer them in the first place.
The US isn't involved in Ukraine like they are in Taiwan. If Ukraine becomes occupied territory, it will be a tragedy but the United States will be okay. If Taiwan is occupied, the entire concept of American economic leadership will be inherently jeopardized and free trade in the Taiwan Strait will probably cease. This would also offer a deeply threatening staging location for attacks on other allies a-la Japan and Australia, whereas the territory of Ukraine is arguably less strategically valuable than Crimea or Georgia, let alone Taiwan. I guess only time will tell.