The following class is the extension of the ProdParmStartUp form in D365 F&O, where I will disable a field in the grid, based on a condition. Therefore users won’t be able to edit that field when that condition is met.

*ProdParmStartUp: This form opens up on the Production order page when we click on the start button

[ExtensionOf(formStr(ProdParmStartUp))]
final class MZNNM_ProdParmStartUp_Extension
{

         [FormDataSourceEventHandler(formDataSourceStr(ProdParmStartUp,ProdParmStartUp), FormDataSourceEventType::Activated)]

public static void FormDatasource_OnActivated(FormDataSource sender, FormDataSourceEventArgs e)
    {
           FormDataSource fds = sender.formRun().dataSource(formDataSourceStr(ProdParmStartUp,ProdParmStartUp));
           ProdParmStartUp     dsTable = fds.cursor();
           FormRun                     fr            = sender.formRun();
           ProdTable                    prodTable;
           boolean                         allowQtyEdit;
           

            prodTable.clear();
           select * from prodTable
                      where prodTable.ReqPOId != ”
                      && prodTable.ProdId == dsTable.ProdId;
           allowQtyEdit = true;
          if(prodTable){
                allowQtyEdit = false;
          }
          fds.object(fieldNum(ProdParmStartUp,StartUpQty)).allowEdit(allowQtyEdit);
          fds.object(fieldNum(ProdParmStartUp,StartUpQty)).enabled(allowQtyEdit);
          //fds.refresh();
         fds.reread();
   }

}