This is a 2 by 2 gridfinity postit note holder for the 3"x3" note size. I used a starter model generated by the wonderful @ABDELat here: Ultimate Gridfinity Bins Collection + Parametric by ABDELat MakerWorld: Download Free 3D Models and added some primitives to raise the floor of the box and remove a sphere for easier access to the postit notes. I've included the 3mf which has those primitives in case you want to tweak their size or position for your own needs, and an stl export if you just want the combined model.

Note: the sphere used to delete the cutout doesn't appear if you preview the model on Makerworld, but it will be visible when you open it in Bambu Studio