With the upcoming 1.36 update, Vector will be redesigned. But, the icon will not be able to be changed, due to $wgLogos->icon being missing from ManageWiki. Please add it on Special:ManageWiki/settings on the "Styling" tab, right before $wgWordmark. $wgLogos->icon is this:
$wgLogos = [ 'icon' => "http://example.com/", ];