I designed this as a two-piece hook. The smaller part screws into the wall, then the larger piece slides down into the smaller one. It may take a little sanding or trimming to get them to fit just right. I recommend printing at a fine resolution (like 0.15mm) for a better fit and overall look.
Supports are needed for the slots and the inside of the back. See supplied .3mf file.
They work surprisingly well. I installed four of these in our kids' bathroom for over a year, and we've only had one fail in that time.
The author hasn't provided the model origin yet.