Hi ! Is it possible to calculate a duration to display it on a graph?

I would like to have a graph that displays the time worked each month. This calculation is based on the "Durée" field of the "Activités" table. Each record in the activity table contains an appointment date. From this appointment date, I extract the duration in the "Durée" field.

I would like my dashboard to show the total duration month by month in the form of a graph.

I was thinking of something like this below but it doesn't work :

Graph formula : 

let filterStart := 'Début du filtre';
let filterEnd := 'Fin du filtre';
select 'Activités'
    where date('Date du rendez-vous') >= filterStart and
        date('Date du rendez-vous') <= filterEnd and
    Statut = 6

Statut = 6 is equal to Status completed

Column 1 : (regroup)

format('Date du rendez-vous', "YYYY-MM")

Column 2 : (sum)

'Durée'

The sum of the durations month by month is not done.

Thanks for your help.