In Apple Mail on Mac how to search for messages I just sent to a single individual?

Search for emails using your own words

When you click in the search field, Smart search suggestions provide recommended searches and show related content.

1. In the Mail app  on your Mac, in the toolbar, enter a phrase in the search field (if it’s not shown, click the Search button  in the toolbar).
2. Type what you’re looking for the same way you’d say it (this is called natural language search). Here are some examples:

• • from nisha
  • from nisha yesterday
  • to joeshmoe
  • to kevin about remodel
  • flagged emails
  • PDF attachments

1. As you type, Smart search corrections improve your results by correcting typos and replacing words with useful synonyms.
2. Press Return.
3. Mail shows the mailboxes being searched in the toolbar above the message list. If there are no results, select one or more different mailboxes in the Mail sidebar or the Favorites bar.
4. When you’re done, click the Clear button  in the search field.

Search for emails in Mail on Mac - Apple Support

But may be easier to click on the Sent folder & sort on Date Sent

Sorry to say, I think you're out of luck.:(