It only works when in the main hand now. Still works if you fire a bow from your offhand while holding a looting sword in your main hand.

Does looting apply in offhand?

Looting affects any kills while holding the enchanted item in the main hand, not only to kills with the enchanted item. ... This allows Looting to work on arrows or thrown tridents, as long as the player is holding the Looting item when the arrow or trident lands.

Does Fortune work on offhand?

While mining, simply place the silk touch pickaxe in any main-hand slots and equip the fortune pickaxe in the offhand. ... However, if you keep the alternative pickaxe in your off-hand and use that shortcut, you can switch between both tools more efficiently.