This was based on the diffuser at https://www.thingiverse.com/thing:1903744.  It has the same internal dimensions (10mm square grid, 9.2mm internal with 0.8mm walls between).  I added added a 0.4mm layer to the top, a 0.4mm recess for the panel, gave it a simple border of 5mm and included a snapfit back.

You should be able to add or remove things from the back (like screw holes, hooks, etc) to easily hang, attach, join to whatever you might want.  Like the original, you'll need to print two of each, glue each half together, then snapfit the panel in between.

I modeled this with 0.2mm layers and a 0.4mm nozzle in mind.  No supports are necessary.  You should print these with the “large” side down (the solid side of the front and the wider/rear side of the back).  I used white for the first 0.4mm of the front and the rest in black, to minimize the light bleed.  I'm sure other color combinations could be exciting!

The result looks much better in person than the photos show.