I have Show slot folders under bones
option under tree top-right corner menu
It says in the user guide that it displays folders:
When checked, slot folders are displayed under the parent bones of the slots contained within them. A slot folder may be displayed under multiple bones if the slots have several parent bones.
However I just see it appends slots folder name to its slots name and I don't see any folder appearing under a bone, it works almost exactly like Show Slot Paths
in the same menu just the folder name is not dimmed and slot moves up under the bone slot order. Please more info Spine Bot