I can get Apple TV on my tv why can I not get Discovery

How to get discovery+ on my tv

Which devices are compatible with discovery+? - Discovery+ Help

Vizio’s SmartCast OS is not listed, so there may not yet be an app for that platform.

If your TV is AirPlay-enabled, then you can stream from your iPhone to the TV.

If you have an Apple TV set-top box (4th generation or later), then you can install the discovery+ app on there.

Having the Apple TV app on your smart TV doesn’t enable other tvOS apps. It doesn’t work that way. The Apple TV app on your smart TV gives you access to iTunes Store content, Apple TV+, and select Apple TV app Channels.