In 4D, when adding a new record, the checkbox in the listbox may not appear if the boolean field (e.g., "Coche") is left NULL, as 4D does not display checkboxes for NULL values. To resolve this, activate the "Map null values to blank values" option in the field properties, which ensures that NULL values are interpreted as empty (unchecked) rather than being hidden.



This is the listbox without checking the option :



After checking the option: