How to hide label in customized contact form? I added a field 'Contact_Catégorie (system name: field_contact_categorie)' to the default 'feedback' contact form.

The field type is List (Text) in which I store a set of "email address | label" in order to redirect the email to the proper recipient depending on the item selected in the list.
That works well!

My issue is about the form display: whatever I choose for the label (Above, On the same line, Hidden, not displayed), the label (Contact_Catégorie) appears in the form.

Any idea?
The Display settings are for the message that is sent.  Setting label visibility in this section would impact how it appears in the email body.

The Manage Form Display are the settings for the form - unfortunately there are no options for label display.  You can alter the form by implementing hook_form_alter() https://api.drupal.org/api/drupal/core!lib!Drupal!Core!Form!form.api.php/function/hook_form_alter/8.2.x  OR if you just want to hide that label you could do it with CSS in your theme, a simple display: none; should work.