Can you get apple music on a Apple HDTV Gen 4 without a subscription?

… all Apple Devices would interface seamlessly.

Alternatively, you can use AirPlay to stream music from Apple mobile devices or Mac computers to the Apple TV box. Use AirPlay to stream audio - Apple Support

Apple Music is a subscription service. So that is only available to subscribers.

The Music app for Apple TV box will also have functionality for iTunes Store purchases (buy-albums), and iTunes Match subscriptions. It also has a few radio stations that are free to stream. All of it is for access to online sources only.

Other music is available from other apps, e.g. Tidal or Spotify, or internet radio stations (through aggregating apps [1] [2] or individual station apps).

Music on a networked computer can be shared to Apple TV through Home Sharing, which uses the Computers app on Apple TV for access, and the Music app on Mac or iTunes app on PC for the Library.

appletv can also access shared media from macs or windows boxs on the same network

Use Home Sharing to share media from a computer to other devices - Apple Support