For those unfamiliar with universal search, it's a feature that allows users to conduct Siri voice searches or text-based searches to find TV and movie content across a wide range of channels. At launch, universal search only supported a few channels, but Apple has been rapidly expanding the feature to encompass additional channels.
Apple maintains a dedicated support document providing Apple TV owners with a full list of content that can be found via Siri using universal search. Unfortunately, universal search is an option largely limited to the United States. In most other countries, only iTunes content is currently supported, while Netflix is also supported in Australia, Canada, France, Germany, and the United Kingdom.