This is a very specific use case, but I had a Dahua camera designed for a Dahua PFA136 adapter that I needed to fit to a Dahua PFA134 junction box as we didn't want to buy and install a new junction box.
The Dahua PFA136 has a larger diameter - this is the part the camera screws into. There are appropriately spaced and positioned M4 heat set insets - I used M4x5x6 heat set insets. This will match the screws that came with your camera, or alternatively you can buy some M4x8 screws and they will work too. You'll likely need to buy at least 3 of these screws as only 3 come with the camera and you'll need 6 in total to do the adapting.
Then there are 3 similarly appropriately spaced and positioned holes which go all the way from the larger diameter to the smaller diameter side for the same type of M4 screws to screw into the junction box.
No guarantees on waterproofness, I'll keep an eye on it. I also printed in PLA, but I imagine PETG would be better given I'm using it in an outdoor environment.
Print with the smaller diameter side on the bed and you won't need supports.
I've attached the Fusion360 file as well, where I've included the following user parameters so you can customise for different types of cameras and junction boxes:
Let me know if any questions and would be keen to see if anyone actually makes this!