macOS users sometimes face issues unmounting volumes, often due to processes like mds
(Spotlight) and revisionsd
causing conflicts. To resolve this, identify the culprit using Activity Monitor or the app Sloth, though Sloth requires repeated authentication. Common solutions include force-ejecting or restarting Finder. Issues reportedly increased with the release of macOS 15 Sequoia.
https://mjtsai.com/blog/2025/02/03/what-to-do-when-macos-wont-let-you-unmount-a-volume/