Macos – How to use Spotlight to search a USB flash drive

First, make sure Applications (and the others that you want) is selected in System Preferences > Spotlight.

If that does not work, it is possible somehow indexing got disabled. In terminal, run the following command:

sudo mdutil -E /

Still, if that fails try deleting the Spotlight index and start indexing it again:

sudo rm -r /.Spotlight-V<TAB>
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
sudo mdutil -E /

On my machine, the Spotlight index was .Spotlight-V100, but I have seen it as other, that is why used tab completion

This article has a lot of good information on maximising the power of Spotlight search. To search by date, for example:

Check the Date Looking for a file that was created during a specific time period? Spotlight has a handle on dates. Typing date:today will bring up files you created, read, received, or opened today. You can also use the date: keyword with yesterday and tomorrow (for the latter, Spotlight restricts its results to iCal events and to-do items).

The latest version of Spotlight also lets you specify more parameters (whether a file was created or modified on a certain date), as well as enter an exact date or a range of dates. For example, you can type created:12/25/07 to find files authored on that date; type modified:<11/30/06 to look for files changed before that date; or type created:1/1/06-12/31/06 to locate files created between these two dates. Unfortunately, date: keywords don’t seem to work correctly all the time.