Some polypanel frames for standard 1088-style 32×32×8 mm LED panels, suitable for e.g. MAX7219 LED dot matrixes from ebay/aliexpress, or Adafruit 8x8 backpacks.
led-matrix-32x32 is a plain 32×32 mm frame, with a friction fit.
led-matrix-32x32x8 is 8 mm deep, and is suitable for matrixes that are soldered directly to the driver PCB (e.g. backpacks).
led-matrix-32x32x8-support is 8 mm deep with stops to prevent the LED matrix from being pushed in too deep. This requires you to install the matrix in the polypanel before attaching it to the PCB, which may not always be possible (and note that despite the name, you can print this without supports).
For more on polypanels, see makeanything.design/polypanels.