In a previous post I suggested this would work, but it indeed does not. The only way to teleport to a new level is to use the Osiris story call CharacterTeleportPartiesToTrigger() and its movie-playing related variations.
To trigger this by using an item, set the item's action to send an Osiris event, and use the following story code:
To get the ITEMGUID_YourTeleportItem_GUID
, select the teleport item, then right-click in the main editor window and select "Copy Type_Name_GUID"). Same for the trigger.
For a tutorial on how to make a basic story, see https://docs.larian.game/Tutorial_-_Implementing_a_Basic_Quest#Building_Your_First_Story