The supplied files for the universal case from CMF and Printables are a good starting point, but not fully designed for 3D printing, as they are modifications of the injection moulded part design. After lots of trial and error, I have settled on a design for a very easy to print rear panel, with accessory disc, lens mount and magsafe option.
I found that the accessory disc included with the phone is so thin with a short thread, that a printed case that was thin enough to be used was incredibly weak and not practical.
For the magesafe one - pause at layer 20 (0.2mm layer height) and stick the magnets in. They'll be covered by a final layer.
I used these magnets: aliexpress.com/item/1005005368496131.html?spm=a2g0o.order_list.order_list_main.5.35891802lvEmgO
Make sure to stick them the right way, peel off the square blue plastic side first.
EDIT: Added new improved accessory disc - 2 parts and uses a M2.5x6mm screw. Push fits together but a drop of superglue will make it solid.
Included files:
The author marked this model as their own original creation.