I need paint to stick together like a flag or cloth.

Hello. I understand from live stream demonstrations (and trying it myself) that you can make a physical painting stick together as one cohesive unit to appear as cloth, such as a flag or curtains moving about.

The method I am referring to is as such: make a square box in paint mode, and then paint inside it. When you grab the entire thing and move it about it will move as one piece.

The problem I'm running into is then I was also shown that if you delete the initial square and keep the rest of the painting, Dreams will know to keep the rest intact as an item. However this doesn't seem to work for me.

Any tips would be appreciated. Thanks in advance, you're all a lovely bunch!