backstage

When you click on the File button in the top left corner you will see a collection of tabs and buttons called Backstage.
The icons, tabs and buttons are slightly different between the different versions.
There is no StartFromScratch option for backstage.

link - learn.microsoft.com/en-us/previous-versions/office/developer/office-2010/ee691833(v=office.14) 
link - github.com/OfficeDev/office-fluent-ui-command-identifiers/blob/main/Microsoft%20365/Current%20Channel/ 

<customUI> 
   <backstage> 
      <tab> 
          <firstColumn> 
             <group> 
   <ribbon> 
   <commands> 

Children

Excel

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui"> 
    <backstage> 
        <tab idMso="PlaceTabHome" label="Home" visible="false"/> 
        <tab idMso="TabOfficeStart" label="New" visible="false"/> 
        <tab idMso="TabRecent" label="Open" visible="false"/> 
        <button idMso="ShareDocument" label="Share" visible="false"/> 
        <button idMso="OfficeExtensionsGetAddinsButtonOnBackstageBelowOpenDivider" label="Get Add-ins" visible="false"/> 
        <tab idMso="TabInfo" label="Info" visible="false"/> 
        <button idMso="FileSave" label="Save" visible="false"/> 
        <tab idMso="TabSave" label="Save As" visible="false"/> 
        <tab idMso="TabPrint" label="Print" visible="false"/> 
        <tab idMso="TabPublish" label="Export" visible="false"/> 
        <button idMso="FileClose" label="Close" visible="false"/> 
        <tab idMso="TabHelp" label="Account" visible="false"/> 
        <button idMso="ApplicationOptionsDialog" label="Options" visible="false"/> 
    </backstage> 
</customUI> 

These buttons were removed (Save As - FileSaveAs, Open - FileOpen, History - HistoryTab, Feedback - OfficeFeedback, Exit - FileExit).
These tabs were removed (Publish - Publish2Tab, Feedback - TabOfficeFeedback).

Word

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui"> 
    <backstage> 
        <tab idMso="PlaceTabHome" label="Home" visible="false"/> 
        <tab idMso="TabOfficeStart" label="New" visible="false"/> 
        <tab idMso="TabRecent" label="Open" visible="false"/> 
        <button idMso="ShareDocument" label="Share" visible="false"/> 
        <button idMso="OfficeExtensionsGetAddinsButtonOnBackstageBelowOpenDivider" label="Get Add-ins" visible="false"/> 
        <tab idMso="TabInfo" label="Info" visible="false"/> 
        <button idMso="FileSave" label="Save" visible="false"/> 
        <tab idMso="TabSave" label="Save As" visible="false"/> 
        <tab idMso="TabPrint" label="Print" visible="false"/> 
        <tab idMso="TabPublish" label="Export" visible="false"/> 
        <button idMso="DigitalPrint" label="Transform" visible="false"/> 
        <button idMso="FileClose" label="Close" visible="false"/> 
        <tab idMso="TabHelp" label="Account" visible="false"/> 
        <button idMso="ApplicationOptionsDialog" label="Options" visible="false"/> 
    </backstage> 
</customUI> 

PowerPoint

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui"> 
    <backstage> 
        <tab idMso="PlaceTabHome" label="Home" visible="false"/> 
        <tab idMso="TabOfficeStart" label="New" visible="false"/> 
        <tab idMso="TabRecent" label="Open" visible="false"/> 
        <button idMso="ShareDocument" label="Share" visible="false"/> 
        <button idMso="OfficeExtensionsGetAddinsButtonOnBackstageBelowOpenDivider" label="Get Add-ins" visible="false"/> 
        <tab idMso="TabInfo" label="Info" visible="false"/> 
        <button idMso="FileSave" label="Save" visible="false"/> 
        <tab idMso="TabSave" label="Save As" visible="false"/> 
        <tab idMso="TabPrint" label="Print" visible="false"/> 
        <tab idMso="TabPublish" label="Export" visible="false"/> 
        <button idMso="FileClose" label="Close" visible="false"/> 
        <tab idMso="TabHelp" label="Account" visible="false"/> 
        <button idMso="ApplicationOptionsDialog" label="Options" visible="false"/> 
    </backstage> 
</customUI> 

Outlook

Info
Open & Export
Save As
Save Attachments
Print
Close
Office Account
Options
Exit