is there an event which is fired, when the wishlist changes? I could need it to show/hide the counter on the wishlist. It should be hidden when my wishlist is empty.
Unfortunately there is no such option to display the counter of wishlist on this condition that if wishlist have some items and hide it if there are no items. You can check the available options from Theme settings >> Shop >> Wishlist.
It requires customization and this is beyond our limitations and support policy.