I don't know the number of US assets in China, but there are a lot of European assets to be seized. Also think of the licensing fees and patents. If the US steals 3 trillion USD from China, do you really think the likes of Qualcomm or Arm are going to receive a cent for their IP licenses? It doesn't matter anyway as China won't be so stupid as to leave all that money in the US if a crisis is developing. The US dollar won't be a "safe haven" currency after what they've done with the Russian reserves.
There are no safe currency left. Dollar, Euro, Yen, Pound are all Western empire members and will do a freeze on China as well. So, China can only rely on its own currency for all exchanges in the future.