Launch support
Native ultrawide support was removed for the launch version. Restoring it was planned for a future update, with no announced release date.
Fullscreen does not change aspect-ratio support
Fullscreen and Windowed Fullscreen are display modes. Selecting one does not by itself add native 21:9 or 32:9 support.
For the normal Graphics setting, see where to find Display mode. For changing how far the gameplay camera is zoomed out, see camera zoom.