I once found a better map, but out of 14 undersea cables in Taiwan, the majority route to Shanghai and HK (naturally, since they are much more important cities financially which usually requires the fastest communications connections), a small number connect to Japan, US, Korea, and Philippines. You don't even need to cut the cables, just disable the routing in China. It would probably create an even worse mess. The Taiwan authorities know of this vulnerability which is why they discuss Starlink, but Tesla Gigafactory Shanghai.
Yes, it would be expected that air superiority would not be an issue in the early stages, but there are some advantages in local sabotage, ie. time to target/detectability/mobility/vulnerability from aerial bombing, etc.