It takes 1 Interact Action
Delving into the official errata (search for Table 6-2 on that page) that accompanied the change, it seems the relevant text was moved to a different section - specifically, the Carrying and Using Items section. Essentially, an object can be Held, Worn, or Stowed. The middle category includes things like weapon sheathes. It takes (usually) one Interact to change how one is carrying an item (the exception being items stowed in a backpack or sack, as described in Table 6-2 under Wielding Items). Thus, sheathing a weapon requires one Interact action. Relevant text from the Carrying and Using Items section, with emphasis by me:
A character carries items in three ways: held, worn, and stowed. Held items are in your hands; a character typically has two hands, allowing them to hold an item in each hand or a single two-handed item using both hands. Worn items are tucked into pockets, belt pouches, bandoliers, weapon sheaths, and so forth, and they can be retrieved and returned relatively quickly. Stowed items are in a backpack or a similar container, and they are more difficult to access.
Drawing a worn item or changing how you're carrying an item usually requires you to use an Interact action (though to drop an item, you use the Release action instead). Table 6–2: Changing Equipment lists some ways that you might change the items you're holding or carrying, and the number of hands you need to do so.