Looking at your example code, it is still missing the autoOpenLyrics attribute.
In order to display the pin icon, your autoHide opening tag needs to have both allowPinning and autoOpenLyrics set to true.
This icon won't appear on any other panels besides the lyrics one.
The allowPinning setting is also used to make the Theater Mode remember (and open on startup) the last used autoHide panel.
But as far as the pin icon is concerned, you only get that on a lyrics panel which is set to be autoOpened whenever a track has lyrics.
<autoHide allowPinning="true" autoOpenLyrics="true">