In Odoo, you can add new filters for the application contact by creating a filter in the "Settings" menu and then assigning the filter to the internal users who need to use it. This will allow the users to select the filter from the list of available filters when viewing the contact application.

To create a new filter for the contact application, go to the "Settings" menu and select the "Filters" option. Then, click on the "Create" button and enter the relevant information for the filter, such as the model (e.g. "contact"), the action (e.g. "[['category_id.name', 'ilike', 'Etudiant(e)']]"), and the context (e.g. "{'group_by':[]}"). You can also specify whether the filter should be set as the default filter for the contact application by checking the "Default" box.

Once you have created the filter, it will be added to the list of available filters in the "Filters" menu. To assign the filter to the internal users who need to use it, go to the "Settings" menu and select the "Users" option. Then, click on the user that you want to assign the filter to, and go to the "Filters" tab in the user form. In the "Filters" section, click on the "Add an Item" button, and select the filter that you want to assign from the dropdown menu.

Once the filter has been assigned to the user, the user will be able to select the filter from the list of available filters when viewing the contact application. The filter will not be set as the default filter for the user unless you have checked the "Default" box when creating the filter.