Many thanks for your quick response. What i am doing i am adding a drop down in grid with visible to false than I am adding following javasciprt on grid initialize event. 

let provider = OutSystems.GridAPI.GridManager.GetGridById($parameters.GridWidgetId).provider;// Get its underlying Wijmo columnlet dropdownWijmoColumn = provider.columns.find(col => col.header === 'Category1');// Extract editor and config from the dropdownconst dropdownEditor = dropdownWijmoColumn?.editor;console.log(dropdownEditor);/*const dropdownConfig = dropdownEditor?.itemsSource ? {    itemsSource: dropdownEditor.itemsSource,    headerPath: dropdownEditor.headerPath,    displayMemberPath: dropdownEditor.displayMemberPath,    selectedValuePath: dropdownEditor.selectedValuePath,    placeholder: 'Select categories',    showSelectAllCheckbox: true,    checkedMemberPath: null} : null;console.log(dropdownConfig);*/let configs = {    itemsSource: ['Accessories', 'Headphones', 'Laptops','Smartphones', 'Printers', 'Storage','Speakers','Smartwatches'], // Static list    headerPath: null, // if using simple array    displayMemberPath: null, // or 'name' if using object array    selectedValuePath: null, // or 'id' if using object array    placeholder: 'Select categories',    showSelectAllCheckbox: true,    checkedMemberPath: null, // optional        valueChanged: function (sender, args) {        // Handle value change and update the grid's data        //let activeGrid = OutSystems.GridAPI.GridManager.GetActiveGrid();        provider.setCellData(rowIndex, columnIndex, sender.checkedItems, true);    }};console.log(configs);let column = new wijmo.grid.Column({    header: 'Category',    binding: 'Sample_Product.Category',     editor: new wijmo.input.MultiSelect(document.createElement('div'), configs)})// Optional: add fake OutSystems metadata for compatibility//column.uniqueId = 'custom_Category1212'; // Custom identifier// When finding OSColumn, fall back to this:console.log(column);provider.columns.push(column);// Optional: Log cellEditEnded events to track changesprovider.cellEditEnded.addHandler(function (s, e) {    const column = s.getColumn(e.col);    const newValue = s.getCellData(e.row, e.col, false);    const oldValue = provider._grid.features.dirtyMark.getOldValue(e.row, column.binding);    // Try to find OSColumn (only works for OutSystems-managed columns)    const OSColumn = provider._grid.getColumns().find(item =>        item.provider && item.provider.index === column.index    );    const isNewValue = oldValue !== newValue;    if (isNewValue) {        if (OSColumn) {            const uniqueId = OSColumn.uniqueId;            provider._grid._triggerEventsFromColumn(e.row, uniqueId, oldValue, newValue);        } else {            console.warn('[Warning] No OSColumn found for column index:', column.index);            // Handle custom column update manually if needed        }    }});// Optional: Log prepareCellForEdit to confirm activationprovider.prepareCellForEdit.addHandler((s, e) => {    console.log('[Edit] Preparing cell for edit - Row:', e.row, 'Col:', e.col);    console.log('[Edit] Cell value before edit:', s.getCellData(e.row, e.col, false));});

Can you please try with this.

let provider = OutSystems.GridAPI.GridManager.GetGridById($parameters.GridWidgetId).provider;

// Configuration for the MultiSelect editor

let configs = {

    itemsSource: ['Accessories', 'Headphones', 'Laptops', 'Smartphones', 'Printers', 'Storage', 'Speakers', 'Smartwatches'],

    placeholder: 'Select categories',

    showSelectAllCheckbox: true,

    checkedMemberPath: null,

    isEditable: true,

    valueChanged: function (sender, args) {

        // Get current cell being edited

        const editCell = provider.grid.hostElement.querySelector('.wj-state-editing');

        const rowIndex = parseInt(editCell?.parentElement.getAttribute('data-row-index'));

        const colIndex = parseInt(editCell?.getAttribute('data-col-index'));

        if (rowIndex >= 0 && colIndex >= 0) {

            // Update grid data

            provider.setCellData(rowIndex, colIndex, sender.checkedItems, true);

            // Manually mark row as edited

            provider._grid.features.dirtyMark.setOldValue(

                rowIndex, 

                provider.columns[colIndex].binding, 

                provider.getCellData(rowIndex, colIndex, false)

            );

        }

    }

};

// Create the new column

let column = new wijmo.grid.Column({

    header: 'Category',

    binding: 'Sample_Product.Category',

    editor: new wijmo.input.MultiSelect(document.createElement('div'), configs),

    dataType: wijmo.DataType.Object // Important for array values

});

// Add the column to the grid

provider.columns.push(column);

provider.cellEditEnded.addHandler(function (s, e) {

    const column = s.getColumn(e.col);

    const newValue = s.getCellData(e.row, e.col, false);

    const oldValue = provider._grid.features.dirtyMark.getOldValue(e.row, column.binding);

    if (JSON.stringify(oldValue) !== JSON.stringify(newValue)) {

        // Force trigger edit event

        provider._grid._triggerEventsFromColumn(

            e.row, 

            'custom_Category', 

            oldValue, 

            newValue

        );

    }

});

document.addEventListener('click', function(e) {

    if (!e.target.closest('.wj-dropdown-panel')) {

        const activeEditor = provider.grid.activeEditor;

        if (activeEditor && activeEditor.hostElement.classList.contains('wj-multiselect')) {

            provider.finishEditing();

        }

    }

});

getting error on value changed have. Is this code working at your enviroment?

Thanks @Manish Jawla - I got initial JS code from that post.