Identify your Apple TV model - Apple Support
The Music app on Apple TV (4th generation or later) will allow you to access all your iTunes Store Music purchases, if signed in with the Apple ID as used for the original purchase, and if you are still registered in the same country.
If you have Apple TV (4th generation or later), with multiple user accounts, then verify that your account is the currently active account. If a different account is active, then the library for the other user get loaded.
If you recently changes countries, then that may make online tracks unavailable, as the iTunes Stores are regional.
Home sharing would make all the shared stacks available. As the home sharing tracks are local and as purchased tracks are not DRM-locked (unless pre-2009), then they should be available without any hinderance. (The Apple Music subscription is different, though: that music is not purchased.)
Use Home Sharing to share media from a computer to other devices - Apple Support