tvOS 11 public beta 3 contains the same features as tvOS 11 beta 4 for developers.
You shouldn’t install the tvOS public beta on your daily driver due to bugs and various issues.
To submit feedback and file bugs with Apple, use the Feedback Assistant app on your iPhone, iPad or iPod touch running a beta of iOS 11.
Next, in Settings → Accounts on your Apple TV type in the same Apple ID that you used to register for the public beta program into at least one of the account options.
Lastly, go to Settings → System → Software Update and turn on the option labeled Get Public Beta Updates, then follow the onscreen instructions to complete enrollment.
The Software Update mechanism on your Apple TV will put up a prompt when a new tvOS 11 public beta is available for download. To manually check for tvOS public beta updates, go to Settings → System → Software Updates → Update Software.
tvOS 11 includes minor improvements such as the ability to synchronize your Home screen layout across multiple Apple TVs via iCloud, automatic switching between Light and Dark mode based on local time, new background multitasking modes, notification support, custom sound support, layered image improvements, right-to-left language support and other tidbits.
tvOS 11 will release for public consumption this fall.