Hi Yuan,
The "open in Unity" grayed out problem can be caused by many things, but generally, the Wwise Launcher has problems finding your Unity project.
Could you let me know if you are using Mac or Wwise? and did you update to the newest version of the Wwise Launcher?
In the meantime, maybe try some of these steps. Or relocate the project to somewhere else on your computer, e.g. transfer it from your external drive to your desktop.
Let me know if this helps!