I made these cool looking shelf supports. They are 150x75mm in size. There are openings in the pattern to accommodate fastening (with some angle). Be careful when fastening the countersunk screws!

I also made a second version that makes it easier to mount it to the wall, but the shelf itself will be a few millimeter from the wall. So decide for yourself what you like most.

Best to print with something like PETG etc to prevent easy breaking when fastening too much.

Have fun! And be sure to like my design when you download it. I also love to see your makes!