Basically, what it says on the title: Pixpets being able to sit/stand on other items that are named as stools, chairs, and benches. Since some of the items are "Stackable:No," like the Mushroom Stool and the Purple Modern Chair, as well as the middle section of the Trellis Arch (Bench).

This could be done by changing their respective Stackable trait to Ground or Partial Ground.