Starting with iOS 14, in order to cast from your iOS device to a second device (like a Chromecast, Roku, or other casting device), you will need to allow Local Network Access for the Tubi app.
You may have seen a pop-up message prompting you to allow or deny this access, and if you're not able to cast now, it's likely you chose "Don't Allow" at the time. That prompt looks like this:
However, you can always change your Local Network Access permissions. To edit Local Network Access permissions for Tubi, please follow these steps:
1. Open Settings on your iPhone or iPad.
2. Scroll down and tap on Privacy.
3. Tap on Local Network.
4. Enable / Disable access to your local network for Tubi. When Local Network Access is enabled for Tubi, you should see this: