Thanks for posting your question, @Raoul. Please be aware that it’s not possible to manually edit document citations; any information you wish to include must be added to the metadata directly on your library. You can go to the item there and either select the option ‘Edit’ via the arrow menu or by hitting Shift + E.
As I mentioned via chat, the inclusion of DOIs is ruled by the chosen citation style and cannot be bypassed unless the information is deleted from the reference metadata (DOI and URLs, which are the usual fallback if no DOI is found). I would not recommend deleting this information from your library; instead you can delete it from the reference in the document by clicking on the bibliography item > Open and editing there. Please be aware this will disconnect said references from their original counterparts, so any other modifications made to the items in your library will not be reflected in the document.