@Momofiore 

Create a rule on the control "demande d'information" by following the below steps:

1. Click on the control "demande d'information"



2. In the top ribbon, click on Add Rule



3. Choose a name for the rule



4. Go to formula and choose equals() from the inline function



5. for the parameters, 1st parameter choose Statut from Named Control and 2nd paratmer will be "demande closed"



6. the formula should be like this: equals(Statut , "demande closed" )



7. then choose the behavior Disable or Hide.

Hello @Momofiore,

you can do it by adding a JavaScript to your form.

1. Give a class name to 'Statut' control .StatutClass



2. Go to control properties of the drop down control.



3. In the Advanced section, select Store Client ID in Java Script Variable as yes.



4. This will open option to name the variable. Name the variable myOptions and click save.



5. Now open form settings and open the Custom Java Script section.



6. Here you can write your script and access the drop down using the ID that you have given in step 3.

NWF$('.StatutClass').change(function(){

if(NWF$('.StatutClass') = 'demande closed'){

NWF$("#"+myOptions).find("option[value='Option 1']").prop('disabled',true)}

});

Hello

I wonder If you can help me to do the step 1:
Give a class name to 'Statut' control .StatutClass ?

Here is a screenshut for Statut

It would be under formatting (see screenshot below). in addition to @DimaHijazi 's suggestion, you should put your on change function within document ready function. See example code below where I am assuming the status field is a text input control. You probably want to re-enable the choice value if the status text is something else as well.