I Googled and found some Access examples that worked for TabHelp, some using the <backstage> section, but no luck

I turned it off manually and checked C:\Users\<userid>\Daddy\AppData\Local\Microsoft\Office\Excel.officeUI

to see how MS did it:

<mso:tab idQ="mso:HelpTab" visible="false"/>
</mso:tabs>
</mso:ribbon>
</mso:customUI>
If you really wanted to, you could maybe try to use VBA to add the above to the file

It's a text file, so you just need to see if it's there, and add it if it's not