There's always room for more discussion, particularly as I don't touch at all on a lot of aspects of the movie, but I have several past answers on accuracy in The Last Duel:

Costumes in the Last duel

The portrayal of Marguerite and Jean De Carrouges in The Last Duel.

THE LAST DUEL claims charges of rape in 14th century France were a species of property crime made against the husband or father of the woman. What was the legal nature of sexual assault in the high middle ages?

I also get at the question in your body text in the SASQ thread, although I have to note that I was being brief there: Froissart's Chronicle is the only place we have an attestation of this penalty. As far as I can tell, there are no definite statements in legal texts of the period as to what would happen. However, we can say that yes, if Carrouges had lost the duel, it would have proven that Marguerite was a perjurer and she would have been punished as one.

You might be interested in the two episodes of The Medievalist Podcast on the movie, one an interview with Eric Jager, author of the book it's based on, and one an interview with Peter Konieczny.