Decide what the drive is for
Android TV distinguishes internal USB storage from removable storage. Google describes internal storage as an extension used by the TV, while removable storage keeps content portable to another device and cannot hold moved apps in the same way.
Choose before formatting. A drive meant to carry personal videos between a computer and television has a different job from a drive intended to support installed apps. The same physical USB stick does not make those storage roles interchangeable.
Protect the existing contents
Formatting erases the drive. Copy any files you need to another location and verify that copy before accepting a format prompt. Identify the drive by its capacity and name so another attached device is not selected accidentally.
Google warns that its generic Android TV steps do not work on every television. Use the manufacturer’s current storage instructions for the actual model and OS. Do not carry a filesystem claim from one box into another merely because both use Android.
Understand the app dependency
When apps or data are moved to an internal-storage drive, that drive becomes part of the viewing setup. Removing it can make the associated apps unavailable. Plan where it will remain connected and whether the port is also needed by another accessory.
After setup, open the intended app and check normal use. A successful format message proves the storage operation completed; it does not establish that every app supports moving or that all existing content has been migrated.
Eject through settings
Use the documented storage eject action before physically removing a drive. Expect content or apps hosted on it to become unavailable after ejection. That state is different from the app being deleted from its store account.
If the purpose changes later, review the consequences of reformatting again. Keep important media separately backed up and do not use an internal app-storage drive as the only copy of irreplaceable files.
Questions answered
Can I use internal storage as a portable video drive?
Google describes internal and removable storage as different roles. Choose removable when portability is the goal.
Why do apps disappear after ejecting the drive?
Apps stored on that drive cannot remain available while its storage is absent.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.