If you edit the cell using inline editing, it works correctly. However, inline editing does not function properly when column grouping is enabled.

<kendo-grid
  kendoGridExpandGroupBy
  id="my-grid"
  [groupsInitiallyExpanded]="initiallyExpanded"
  [(expandedGroupKeys)]="expandedGroupKeys"
  [columnMenu]="{ filter: true }"
  [kendoGridBinding]="advanceGridData"
  [hidden]="!isAdvanceGrid"
  [ngClass]="{'report-display-none': !(groups.length > 0 || aggregates.length > 0) }"
  [filter]="state.filter"
  [navigable]="true"
  [groupable]="true"
  [height]="'auto'"
  [resizable]="true"
  [skip]="state.skip"
  class="grid-page-number"
  [filterable]="isFilter"
  [sortable]="{mode: 'multiple'}"
  [sort]="sort"
  [group]="groups"
  (cellClick)="cellClickHandler($event)"
  (cellClose)="cellCloseHandler($event)"
  (filterChange)="applyFilter($event)"
  (sortChange)="sortChange($event)"
  (columnVisibilityChange)="checkHiddenColumns($event)"
  (groupChange)="groupChange($event)"
  (dataStateChange)="dataStateChange($event)"
  (keydown)="keyPress($event)"
  (excelExport)="onExcelExport($event)"
  [kendoGridSelectBy]="selectedKey"
  [selectedKeys]="excludedRow"
  [selectable]="{enabled: true, checkboxOnly: true}"
>
  <kendo-grid-column
    *ngFor="let header of headers"
    [field]="'['' + header.field + '']'"
    [title]="header.title"
    [filter]="header.filter"
    [format]="header.format"
    [headerStyle]="{'font-weight': 'bold'}"
    [filterable]="header.isFilterable"
    [width]="header.width"
    [hidden]="header.hidden"
    [locked]="header.locked"
    [style]="{
      'background-color': header['backgroundColor'],
      'color': header['textColor'],
      'text-align': header['alignment'],
      'border-bottom': header['backgroundColor'] ? '1px solid #A9A9A9' : ''
    }"
  >
  </kendo-grid-column>
</kendo-grid>
 
public cellClickHandler(args: any) {
  const { sender, rowIndex, columnIndex, dataItem, isEdited, column } = args;
  this.isEditingCell = true;
  this.currentlyEditingDataItem = dataItem;
  sender.editCell(rowIndex, columnIndex, this.createFormGroup(dataItem, column));
  this.editedRowIndex = rowIndex;
}

public createFormGroup(dataItem: any, column): FormGroup {
  const formGroup = this.formBuilder.group({});
  const propertyName: string = column.field;
  const normalizedKey = Array.isArray(propertyName) ? propertyName[0] : propertyName;
  formGroup.addControl(normalizedKey, this.formBuilder.control(dataItem[normalizedKey]));
  formGroup.valueChanges.subscribe(formValues => {
    Object.keys(formValues).forEach(key => {
      const normalizedFormKey = Array.isArray(key) ? key[0] : key;
      dataItem[normalizedFormKey] = formValues[key];
    });
  });

  return formGroup;
}

public cellCloseHandler(args) {
  const { formGroup, dataItem, column } = args;
  if (!formGroup.valid) {
    args.preventDefault();
  } else if (formGroup.dirty) {
    this.editService.assignValues(dataItem, formGroup.value);
    this.editService.update(dataItem);

    if (this.editedRowIndex !== -1) {
      const fieldName = column.field.replace(/[[]']+/g, '');

      Object.keys(formGroup.value).forEach(key => {
        this.headers.forEach(item => {
          if (fieldName === item.title) {
            const updatedValueAsString = formGroup.value[key];
            if (item.dataType === 'Float') {
              this.updatedValue = parseFloat(updatedValueAsString);
            } else if (item.dataType === 'Integer') {
              this.updatedValue = parseFloat(updatedValueAsString);
            } else {
              this.updatedValue = updatedValueAsString;
            }
            this.advanceGridData[this.editedRowIndex][fieldName] = this.updatedValue;
            this.total = aggregateBy(this.advanceGridData, this.aggregates);
          }
        });
      });
    }
  }
}

It should replace the original value from this.advanceGridData with the edited value while grouping the column.
When We do grouping the inline edited cell doesnt save the values in kendo cell