An action camera mount to fix on an DIN ISO 5422 M20 tow mount hook. Those are typical for many German car makes. Might apply for others. My tow hitches are about 53,50mm wide and 11..13mm in diameter.
Nice is that this one is really sturdy and the camera can be taken off together with the hook.
Amazon Basic PLA
Printed fine without supports; on an Creality Ender-3 (bed size 235 x 235mm²) using Cura 4.0, you can print both the upper and the lower part in one go using Cura's "Print Setting" = "One at a time" and some rotation and movement of the models. See last image.
100% infill is intended as I did not manage to print only the GoPro connector solid (what it should be).
Mounting to tow hook
I recommend to fix this thing to the tow hook using three M5 screws, three nuts from https://www.thingiverse.com/thing:155474 and open M5 nuts inside them.
Reason is that you might want to remove the mount from the tow hook without tools in case you just recorded some real action on a track day.
Using FreeCad, the .FCStd file is included. It holds both parts which I split using an element in the "Split" folder.
It did not manage to make additional rounding of the corners as FreeCAD either trashes the model or removes it completely.