>>> Only applies for Idea Intellij IDE
Okay, I finally figured out why the option is not available (greyed out).
It should be the inconsistency problem between the old version of the flutter plugin and a new one.
You might experience this issue if you created the project with a relatively old version flutter engine, and open it with a new version flutter plugin.
To know what happens and how to resolve it:
So you know how to fix the issue:
Rename the iml file to (YourProjectName_android.iml) That would instantly make the menu highlight again!