It is a bracket I designed for holding up a paper model of a bridge but it should be able to hold more weight.
The top hole is slanted for easy screwing into the wall.

Here is the link to Tinkercad if you want to remix it:
https://www.tinkercad.com/things/2xrKyIhrVyg

Print instructions

Print on the side
No supports needed
10+% Infill
2+ Perimeters (print with what you need)