Strong shelf brackets designed to hold a 300mm deep shelf board! These were made with Fusion 360's topology optimization feature for the unique look, but they're definitely not too shabby in the strength department, either. Each one holds my full weight and then some.
Make sure to mount them to you wall securely! Find a stud or, in brick walls, use proper wallplugs. Your mounting solution will probably fail before the bracket does!

Here's my process of designing it!

Print instructions

Easily fits diagonally on a MK3 bed
For extra strength, add a modifier mesh and increase infill around the upper mount

I printed mine in PLA, but any material with good layer adhesion will work (e.g. PETG)