If an update is listed, apply it without a second thought. If it says no Outlook updates are available, you are good to go.
The root cause for this predicament varies, and therefore the fix is usually a matter of trial and error. In the unlikely event the Spotlight index is corrupted, you may have to go the extra mile getting the feature to re-index messages. One of the possible reasons is that Spotlight hasn’t yet indexed your data if you have recently added a new profile to Outlook for Mac. It’s hard to say why exactly this adverse situation might occur, but it makes some emails slip under the radar when you run a search. If so, the Mac’s Spotlight feature is blocked from searching that location.
How to fix Outlook search problem on Mac.