Which Uncharted game was released as a standalone expansion for Uncharted 4?

The standalone expansion released for Uncharted 4 is Uncharted: The Lost Legacy. It was developed by Naughty Dog and published by Sony Interactive Entertainment in 2017.

The project began as downloadable content for A Thief's End, but its scope expanded considerably during development. Rather than following Nathan Drake, the game puts Chloe Frazer in the lead, with Nadine Ross as her partner. Their mission is to recover the Tusk of Ganesh in India's Western Ghats while stopping the warlord Asav from provoking a civil war.

The Lost Legacy is connected to Uncharted 4 through its characters, technology, and timeline, but it works as a self-contained adventure. It was released for PlayStation 4 on August 22, 2017, in North America. A remastered version later appeared with A Thief's End in the Uncharted: Legacy of Thieves Collection.

The other options are unrelated spin-offs or handheld and card-game titles, not expansions of Uncharted 4.