I know that the word count will depend on the tools (MS Word, Libre Office, Online tools?).  To get a consistent word count, I ask my students to submit their weekly homework via Canvas and use the word count shown on the Rich Text Editor for reference.

However, when I grade the work through the speed grader, I cut points from students when the word count shown on speed grader are lower or greater than the agreed limit.  I believed that Canvas word count at the two places are the same. I was wrong.  These can differ significantly in some cases.  I don't bother to investigate reasons at this point. It is good to share the problem and my temporary solution here. If you have a more convenient solution, please let me know.

For work that appears to be under or over the agreed length, I quickly copy the text in speed grader and paste in the comment box which is also a rich text editor.  If the word count value is still outside the agreed range, I note the value in the box and make a comment that I cut points.  Otherwise, I noted the new value of word count and grade it normally.

This appears to be extra work on the instructor side but it actually very efficient (or arguably the most efficient). The penalty of going under/over the range makes the answers much easier to grade and majority of the students will conform to the rule.