I wanted a GoPro mount that would be as small as possible on my rucksack strap. Therefore I didn't want to use the usual GoPro pivot and opted for a shim that orients the camera to the front. The strap gets sandwiched by the shim and mount with two cable ties. The GoPro can be fixed with the standard GoPro thumb screw or with a M4x20 socket head screw and a M4 nut.
Print instructions:
PETG, 0.3 mm layer height
Small supports needed for rounded parts of the GoPro mount
The different parts are glued on the plate.
Update 2022/10/12:
Added separate stl files for the GoPro mount.
The author marked this model as their own original creation.