Within Final Cut Pro, use the "Consolidate Library Media" command to ensure all video files are stored inside the library file on that drive.
: Final Cut Pro relies on a complex SQLite database (the Library) that requires specific macOS file systems (APFS or HFS+) for "journaling." Running the app in a "portable" environment or from incorrectly formatted drives can lead to permanent database corruption. final cut pro 1046 dmg portable
The Final Cut Pro interface is divided into several sections: Within Final Cut Pro, use the "Consolidate Library