Spotlight problems
Almost every macOS upgrade triggers a full re-index. For a few hours to a day, search is genuinely unreliable — and then usually fixes itself.
A major upgrade invalidates the Spotlight index and rebuilds it from scratch. On a large disk that is hours. During it, results are partial and the Spotlight menu may show a progress bar.
Check whether that is what is happening:
mdutil -s /and look for mds or mds_stores near the top of Activity Monitor.
Rebuild explicitly:
sudo mdutil -E /Then leave it alone for a few hours.
Check the exclusion list — System Settings → Siri & Spotlight → Spotlight Privacy. Upgrades occasionally leave entries there, and Migration Assistant can carry old ones over.
Also check the category checkboxes in the same pane. An update resetting them is rare but not unheard of, and an unchecked category removes those results entirely.
Upgrades sometimes reset privacy grants. If the Terminal or a search tool suddenly cannot read parts of the disk, re-grant Full Disk Access in System Settings → Privacy & Security. The app must be relaunched afterwards.
A tool that maintains its own index does not depend on Spotlight's rebuild, and one that persists an FSEvents position can replay exactly what changed during the upgrade instead of rescanning. In practice that means search keeps working through the window where Spotlight is rebuilding.
A few hours on an SSD; longer on a large or mechanical drive. It runs in the background.
sudo mdutil -i off / disables indexing, but search stops working entirely. Better to let it finish.
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