Can't disable session state protection on Oracle APEX 18.1.0.00.45 for Dynamic Actions updating Page Items

From my own experience: it appears that P5_EXAMPLE_ITEM is a text item which has the "Read only" property set to "Always".

If that's so, set the item type to display only (because the first combination - a read-only text item - is nothing but a display only item with "save session state" set to "no").