[SalesForce] APEX – Get ContentDocumentLink when deleting file (with ContentDocument)

I have an object 'ClientContract__c' with affiliated files. When adding a file, this changes a technical checkbox field on the parent object.
I would like to override this technical field if there are no more affiliate files.

When deleting a file, the same trigger is not called (when updating and inserting, the trigger call is on ContentDocumentLink object while when deleting it is a trigger on the ContentDocument object).

Can you help me to
Retrieve the ContentDocumentLink from the trigger on the ContentDocument object and if there is no file pass my technical field to false?

My code on ContentDocument object :

if(Trigger.isDelete){
    Set<Id> SetOfCd = new Set<Id>();
        List<ID> opportID = new List<ID>();
    for(ContentDocument cd :Trigger.old){
        SetOfCd.add(cd.Id);
    }

    for (ContentDocumentLink files: [SELECT Id,LinkedEntityId FROM ContentDocumentLink WHERE ContentDocumentId IN:SetOfCd]) {
        if(!(opportID.contains(files.LinkedEntityId)))
            opportID.add(files.LinkedEntityId);
    }

    List<ContratClient__c> cc = [SELECT Id,FichierLie__c FROM ContratClient__c WHERE Id IN :opportID];
}

My code on ContentDocumentLink object when the file is upload :

if(Trigger.isInsert){
        List<ID> opportID = new List<ID>();

        for (ContentDocumentLink files: Trigger.new) {
            if(!(opportID.contains(files.LinkedEntityId)))
                opportID.add(files.LinkedEntityId);
        }

        List<ContratClient__c> cc = [SELECT Id,FichierLie__c FROM ContratClient__c WHERE Id IN :opportID];

        for (ContratClient__c contrat :cc) {
                contrat.FichierLie__c = true;
        }

        update cc;
        system.debug('Contrat:' + cc);

    }