Troubleshooting & messages · Drive connection and drive messages
Why does Storage Studio say some apps are unavailable when the drive is disconnected?
Short answer: Moved apps run from the external drive, so they can't open while it's unplugged. Reconnect the drive, or move an app back first if you need it away from your desk.
Apps you moved to the external drive run from that drive. While it's unplugged, macOS can't find them, so Storage Studio counts them as unavailable and tells you to reconnect the drive to use them.
Nothing is broken. Plug the drive in and they open as usual. If you need an app while away from the drive, move it back to your Mac from the Apps window first.
See moving apps back.