Hi @ArnaudA! Welcome to the Community-- happy to have you here 
My initial thought would be a report too, but I can see the disconnect when our end goal is a list. @karstenkoehler & @JBeatty provide some great comments in this thread explaining how you can create a calculation property based on the total number of deals associated with another object. That may be a good place to start and then see what options you have for filtering by that order date
Best,
Kennedy