Not Handed in
It is very apparent in a hand in folder who has not handed in their work, but there is a situation where this has to be followed up in a bit more detail: If a handing in is attached to Learning goal and is part of the portfolio method, you as a teacher will not have a display of missing submissions in the Portfolio tool, because here only the assignments that have been handed in are displayed.
It may therefore be prudent to do a hand in on behalf of these students by using Hand in on behalf of and enter a title so an empty document is created (possibly with some comments):

You can then note that no work was handed in by this student, so it clearly appears in the portfolio.