Currently, furniture within houses is saved to that house and cannot be removed or stored individually.
This is usually fine because most furniture items are available in the shop for you to purchase and place. However, some furniture is no longer available for purchase; for example, the 2019 Christmas Tree cannot be moved and can only stay in the house that it was placed in.
Please do not sell these exclusive furniture items, trade away, or sell the houses they are in unless you are sure because you can not get them back. Even if you attempt to use the undo button, it will not return it as they are no longer available for purchase.