The particularity of the safe page mode editing compared to the simple form mode, and that it does not allow the modification.
As a result, cards are read-only.
To go into secure form mode, go to the table options , and click Enter safe page editing mode :
The icon, representing a padlock and preceding the name of the table, makes it possible to indicate to all the members of the notebook that this table is in secure form mode :
Exit safe page editing mode