Reindex Spotlight when search finds nothing

Rebuild the search index.

1. Check that indexing is on:

   mdutil -s /

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2. Erase and rebuild the volume's index:

   sudo mdutil -E /

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3. You can also open System Settings → Siri & Spotlight → Search Privacy, add a folder then remove it to force a reindex.
4. Indexing can take several hours and temporarily slow the Mac down.