your file "rod.fcstd" is an Asm4 file, but the file "pendulum.fcstd" is not (I don't know wheter its Asm3 or Asm2+). So you probably created an Asm4 file, and then tried to assembly it with something else.
Please try to open the attached file "pendulum_Asm4" (in the same directory as "rod").
what workbench did you use ? In Asm4 there are no more macros, they should be toolbars now. You can try to download the Asm4 files (https://github.com/Zolko-123/FreeCAD_Assembly4) and move - or copy or link - the Mod_Asm4 folder to the folders where the workbenches are (oups, I use Linux, they are in ~/.FreeCAD/Mod/). You should have the Asm4 workbench installed.I tried to follow your instructions. I create the part with the new model macro. I create the assembly wih the new model macro; create the sketch with LCSs and import the part with the insert external part macro. When I try place the part, it highlights the part but I don't see the place linked part dialog box.