First, insert a rectangle in the PPT, select the shape rectangle in the Insert tab, and draw
Right-click to set shape format, choose the effect you want, here I chose a solid color fill, no Line color
The resulting effect is as shown
Double-click the graphic, the menu bar Insert shape has an edit shape, click to select the edit vertex, then the graphic will appear around the black box
Hold down the black square to the freeform (right-click to add or remove vertices), press Ctrl+shift to copy pictures vertically
Be patient with this.
Online pictures If you have ready-made, do yourself a little trouble