Xbox One storage is full or games will not install

The checks in more detail

Uninstall games and apps you have finished, since you can download them again from your library without losing saves, which are stored in the cloud or on the console. Also remove old captures and clips, which are found in the Captures app and add up. Delete the Blu-ray or media apps you never use. To add an external drive, connect a USB 3.0 drive to a USB port on the console, and the console offers to format it for games and media; Microsoft sets minimum requirements for the drive size and says it must be USB 3.0 or later, and that formatting erases everything on it.

EaseUS's guide for external drives that do not work lists common faults: a drive on a USB 2.0 port or hub, a cable that is too long or weak and a drive that needs its own power. A drive used by the console can only be used on that console until reformatted, but you can move it to another Xbox One and its games work with the same account. You can move games between the internal and external drives from the Manage menu. Keep some free space on the internal drive for updates and the system. If the console still says storage is full after deleting a lot, restart it and clear the cache by turning it off and unplugging for a minute.

A failing internal hard drive, signalled by slowdowns and errors, can be replaced with a larger drive by a technician. The original Xbox One is a loud, heavy console, and its hard drive is a mechanical one, so moving big games to an external SSD also makes loading faster and quieter. An external SSD with USB 3.0 gives shorter loading times than the internal hard drive. If you plan to keep the console for years, a larger external drive is the most useful single upgrade, and the same drive works on a newer Xbox for older games.