God's right-hand man

 Peter pissant (It's a pseudonym) resides on Microsoft. He isn't paid, he just berates others for the feeling he gets knowing more than you.

But I digress...In Excel (prolly word as well) there are / should be 2 x's, one is "close program"
and the other, "Close (current) workspace" (sheet, document, whatever) as illustrated by this little pic on Google that I stole a piece of:

 And if it isn't there, Peter denies its existence.

grrr.

Hang on, there's a macro you can create (where's the damned built-in button?)

https://turbofuture.com/computers/How-to-Create-a-Macro-Button-to-Save-Close-an-Excel-Workbook

Progress!! Nervous, fidgety, paranoid Progress...

https://excelribbon.tips.net/T011315_Closing_Excel_when_Closing_the_Last_Workbook.html

https://contexturesblog.com/archives/2013/04/25/close-all-files-in-excel-2013/

*I* just added, perforce, a "Custom Toolbar" with the single command "Close" (X), except it's on the very left-hand side of the screen, and it's custom, so it's not like you could teach someone to use it (It's a built-in command, it exists, but it's really hard to find or to put into a toolbar.)

"Close" (doesn't work), "close window," "close-all," close yada

This next bit might be for Microsoft Word (it doesn't actually say what it's for)