The War Powers Resolution of 1973 put lots of restrictions of U.S. presidents for war declaring:
The War Powers Resolution (also known as the War Powers Resolution of 1973 or the War Powers Act) (50 U.S.C. ch. 33) is a federal law intended to check the U.S. president's power to commit the United States to an armed conflict without the consent of the U.S. Congress. The resolution was adopted in the form of a United States congressional joint resolution. It provides that the president can send the U.S. Armed Forces into action abroad only by declaration of war by Congress, "statutory authorization", or in case of "a national emergency created by attack upon the United States, its territories or possessions, or its armed forces".
However, as mentioned in this answer, president could still violate the War Powers Resolution of 1973. Recently President Biden said in an interview that U.S. will send troops to Taiwan if "there was an unprecedented attack". It gave people an impression that POTUS has such a power by himself.
So my question is (noticing that POTUS is the commander in chief of U.S. arm forces):
Technically, can (and how can) the president of U.S. order troops to help defend Taiwan under China's invasion without congress' approval?