I have a simple test Customization for Excel backstage, but the problem is the UI Only shows after opening a workbook, How do I make it show in the opening backstage UI? Is this approach outdated, I can’t find any new articles or documentation updates about backstage customization.

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui"   onLoad="OnLoad">
  <backstage onShow="OnShow" onHide="OnHide" >
    <tab idMso="TabRecent"   visible="false"  >
    </tab>
    <tab idMso="TabSave"   visible="false" >
    </tab>
    <button idMso="FileSave" visible="false"/>
    <button  id="btnSave" getVisible="WPFUIVisibility" label="Save" imageMso="FrameSaveCurrentAs" insertAfterMso="TabSave"   onAction="onSaveUI"/>
    <button  id="btnOpen" getVisible="WPFUIVisibility" label="Open" imageMso="FileOpenDatabase" insertAfterMso="TabInfo" onAction="OnAction"/>
  </backstage>
</customUI>