I know that there is a keyboard shortcut that lets you open the emoji palette while you are typing, but I could not find any shortcut that lets you close the palette.
So right now, whenever I finish adding my emoji I manually close it by tapping on the top-left red X button. This is quite troublesome, so is it possible to close it via the keyboard shortcut?
I use Mojave on 2017 MacBook 12'.
The behaviour is somewhat awkward.
Even the Menu option doesn't toggle it on/off, only on.
If you simply double-click your emoji without doing anything else, it doesn't even bring the window to the front...
..so, the only real option is after you open it, click its header bar [while you're over there anyway to grab your emoji]
It will then respond to Cmd ⌘ W the same as any other window.
Of course, if you forget, it will close the window you were working in :\