Hi Antoine,
after importing the iges file, make sure that the individual parts are set to "visible" (the little eye symbol in the object editor), also please check that the main scope is set visible (by clicking on the icon in the object tree you can show and hide objects from the 3D view). At last you could try to use the "Reset Zoom" button in the 3 D Window.
Here is a little video for what I explained.
2022-10-20_09h54_26.mp4
Kind regards,
Hedi