BuddyPress.org

I found I have to declare it in my theme as noted here https://buddypress.trac.wordpress.org/ticket/6570:

bp_set_theme_compat_feature( 'legacy', array(
	'name'     => 'cover_image',
	'settings' => array(
		'components'   => array( 'xprofile', 'groups' ), /* or you can only use array( 'xprofile' ) to restrict the cover image to users */
		'width'        => 1170,
		'height'       => 225,
		'callback'     => 'swifter_theme_cover_image', /* function that will return to BuddyPress the css to attach to the theme_handle */
		'theme_handle' => 'swifter',
	),
) );