There are many models of the Apple TV, dating all the way back to its original release in 2007. However, not all models give access to the App Store, which is required to download White Walls.
The oldest model that will work with White Walls is the Apple TV HD, released in 2015. This model does have some performance issues with GIFs and larger files, so we recommend using an Apple TV 4K (2017) at minimum for the best viewing experience. Just remember: the newer the model, the better the performance.
You can identify Apple TV models here:
https://support.apple.com/en-us/101605