Minecraft wiki entry for Heads-up_display, associated text: Players can dual wield allowing a second item to be shown on the left (or right if the player's main hand is set to "left"), along with an additional hotbar slot on the same side. Both the slot and the item are shown only if it contains an item, which can either be added using the GUI or by pressing "swap items." In Java Edition, it shows the off-hand slot with the items equipped on the left of the hotbar. In Bedrock Edition, this is not the case although the item is still equipped in the off-hand slot.