Cancel Super Lookup Call D365 , X++

 write this code in the OnLookup event handler after your lookup code.

 FormControlCancelableSuperEventArgs ce = e as FormControlCancelableSuperEventArgs;
            ce.CancelSuperCall();

For example see below code :

 [FormControlEventHandler(formControlStr(InventJournalMovement, InventJournalTrans_ItemId), FormControlEventType::Lookup)]
    public static void InventJournalTrans_ItemId_OnLookup(FormControl sender, FormControlEventArgs e)
    {
        InventJournalTrans InventJournalTrans = sender.formRun().dataSource("InventJournalTrans").cursor();
        inventJournalTable inventJournalTable = inventJournalTable::find(InventJournalTrans.JournalId);
       
            Query query = new Query();
            QueryBuildDataSource queryBuildDataSource;
            QueryBuildRange queryBuildRange;
            SysTableLookup sysTableLookup =
            SysTableLookup::newParameters(tableNum(InventTable), sender);
            sysTableLookup.addLookupField(fieldNum(InventTable, ItemId));
            sysTableLookup.addLookupField(fieldNum(InventTable, NameAlias));
            queryBuildDataSource = query.addDataSource(tableNum(InventTable));
          //  queryBuildDataSource.addRange(fieldNum(InventTable , PowerPlantItem)).value(enum2Str(NoYes::Yes));
            sysTableLookup.parmQuery(query);
            sysTableLookup.performFormLookup();
//To cancel super call add these two lines
            FormControlCancelableSuperEventArgs ce = e as FormControlCancelableSuperEventArgs;
            ce.CancelSuperCall();
        
       
    }