Simple honeycomb end pieces I made for a monitor stand. Dimensioned for 1.5 cm thick plywood or similar. About 17.5 cm deep.

I uploaded a version without and two versions with brackets. I also made a middle brace that can be put in the back to avoid sagging shelves if you make it very wide.

Print instructions

I upped the bed temp to try to avoid warping in the corners. You can also try to warm the bed longer before printing to ensure it is properly warm all over, and print in an enclosure.
I printed in PETG to avoid sagging on a hot summer day, and used three perimeters for added strength.