Inline Editing is not available after override the standard Edit and Delete buttons in salesforce object
Whenever we override Standard Buttons (“Edit, Delete”) of any object in sales force then inline editing of that object is removed so we can’t able to do inline Editing from detail page of that respective object record.
we can easily check either the standard/custom object has been override any of the salesforce buttons.
For standard objects: Go to Setup -> Customize -> <Objects> -> Buttons & Links, and note the “Overridden” checkbox next to the ‘Edit’ standard button.
For custom objects: Go to Setup -> Create-> Objects | <Objects>, scroll down to the Buttons & links section, and note the “Overridden” checkbox next to the ‘Edit’ standard button.