J'ai essayé sur une page wordpress, aucun soucis elle s'affiche. Par contre sur une page personnalisé rien ne s'affiche. j'ai testé avec Textfield, Embed et WYSIWYG rien ne fonctionne.
So, you want to dynamically insert an iframe into a template rather than a page, where the iframe code is stored in a custom field?
That isn't possible directly, but there is a workaround, where you use a custom field to store the value for the src attribute of the iframe and then construct the iframe element dynamically, using a shortcode to provide the value for the src attribute from the custom field.
Assuming you are using the block editor you could use a Custom HTML block or Fields and Text block in HTML mode.
Assuming that you have a custom field "iframe-src" that stores the url, your HTML would look something like