Finding things in Finder · Spotlight, tags and file details
Does Spotlight indexing my external drive get in the way of Storage Studio?
Short answer: Not for moves — Spotlight and other macOS housekeeping are ignored when checking what's using a folder. Spotlight can briefly keep a file open on the drive and delay an eject; wait a moment and try Eject fast drive again.
For moves, no. When Storage Studio checks which apps are using a folder before moving it, macOS's own housekeeping services such as Spotlight indexing are left off the list — they can't be quit and don't interfere with the move.
Where you may notice Spotlight is ejecting. If indexing still has a file open on the drive, the eject can fail with a message that files are still in use, and Storage Studio lists what's holding the drive. Wait a moment for indexing to settle and try Eject fast drive again.
Storage Studio's own background work is designed to step aside for you in a similar way, so it doesn't compete with what you're doing.