Exporting from Inventor

File > Export > CAD Format > Save as type: STL Files (*.stl)

Note that Inventor does not yet support .3MF files, which are typically preferred due to smaller file size.

While exporting, click Options to change export resolution. Before committing to your export, check the output with Preview. Further refinement can be made using Custom Resolution, but High Resolution typically yields an efficient, clean part export.