Explanation
The Excel Application Scope activity interacts with a Microsoft Excel file in the following way: it works with xls and xlsm files and Excel must be installed. The Excel Application Scope activity opens an Excel workbook and provides a scope for Excel activities. When the execution of this activity ends, the specified workbook and the Excel application are closed2. The Excel Application Scope activity can work with xls (Excel 97-2003 Workbook) and xlsm (Excel Macro-Enabled Workbook) file formats3. However, the Excel Application Scope activity requires Microsoft Excel to be installed on the machine where the automation is running, as it uses the Excel interop assembly4. Therefore, the Excel Application Scope activity cannot work with xlsx (Excel Workbook) files or without Excel installed.
References: Excel Application Scope, File formats that are supported in Excel, and Excel Application Scope - UiPath Activities Guide from UiPath documentation and Microsoft support.