Apple has this week released tvOS 15.4 for Apple TV HD and Apple TV 4K, with the main new feature being the support for captive WiFi networks. This means, like HomePod can now, the Apple TV can connect to WiFi networks where you need to log in, such as those in hotels, universities and more.
The Apple TV will use a local iPad or iPhone to help you connect to the WiFi network. This update also adds the “Up Next” queue to the video player as well as allowing you to use an Apple Watch to authorise any in app purchases.
tvOS usually updates automatically, but if you want to manually upgrade, it can be done so by going to Settings > System > Software Update.