Hi Mary,
When you were on Windows 7, you must be using older version of Office. Based on my search, the option you mentioned (File>New>New from Existing) is available in Excel 2010. Here’s the screenshot for your reference.
In the newer version, this has been changed. Now, to create the workbook from an existing, one must open the desired workbook and save as with the new name. This will keep the version of the previous workbook with all its link to the older workbook and the new workbook will have new version.
Here’s an article for reference: Create a new workbook
If you have any suggestion or you would like to see the old interface in new Office version, you can provide your feedback in Excel UserVoice and let the team know about your requirement. UserVoice is the best way to give the feedback to Product Group as it’s actively monitored by them and many new features have been implemented from our customers feedback.
We appreciate your understanding.
Regards,
Neha