Shelf bracket - 200mm x 200mm (just under 8" x 8") legs, 25mm (1") wide. Great for a 230mm (9") deep shelf. Could be scaled down, but smaller screws may need to be used. Printed a 100%, the screw holes are perfect for standard drywall screws.
Bracket pictured was printed with 20% infill and a .16mm layer height. Excellent print on a Creality CR-6 SE in PLA without support. Note that there is one short section that prints with a 67.5° overhang. Support may be needed if your printer can't handle that angle.
Inside corner screw holes are not accessible straight on- it is recommended to predrill the hole and use a long screwdriver to drive the screw.
Printed in PLA at 20% infill, the single bracket held well stacked with 16 pounds (7.25 kg) of weight. Two or more brackets and an attached shelf should increase stabilization. Your results may vary.