When you hold Q while hovering above an item in your inventory, you can drop items continuously. When you try to do that while you're in the inventory of a chest/enderchest/furnace/barrel, you can't drop them continuously.
is blocked by
MC-118107Action of some keys continuously repeat if you hold them
is duplicated by
MC-178549Inconsistency with dropping items from inventory
MC-181043Can't drop items fastly when container is open
MC-222838Inconsistency: Holding down Q (or Ctrl+Q) rapidly drops items from player inventory, but not from block inventories
MC-255409Dragging Ctrl+Q doesn't work in every container