Home Sharing not working on Apple TV and Mac

1. Activating Home Sharing asks for an Apple Account. These should match for both devices, else the library won’t be discoverable. The library should have at least one item.
2. Both devices need to be on the same home network. For Wi-Fi, that means the exact same SSID network name. If your router makes a distinction between the 2.4 GHz band and 5 GHz band through separate SSID network names, then devices on one part cannot communicate with devices on the other part. It is recommended to have the router combine both segments under one name as one logical network (together with the wired). Recommended settings for Wi-Fi routers and access points - Apple Support

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

What is the version system software (macOS) on the computer?

What is the version system software (tvOS) on the Apple TV box?

Home Sharing can work with media files in any location that is accessible to the Mac, including external disks and network drives.

The Library and the Media Folder are two separate properties. Be sure not to equate them in your mind.

The Library is the database, and should reside in the home folder on your boot drive. If the Mac boots up without access to/finding the library, then it will create a new empty one.

The Media Folder defaults to somewhere in your home folder on your boot drive, but can be moved anywhere. If you move it to a different Volume, confirm that in the app settings, else a new Media Folder will be recreated. Placing items in the media folder will not add them to the library; you will have to add to library from within the app.

The TV app settings (same for iTunes application) has two settings that should be of interest to anyone changing the defaults:

You may want to uncheck those, if you use your own folder structure, and if you add files to the library, when they are already in their intended location.

The Library on the Mac maintains links to each file of library content in a library database. So check if the link works by playing a few seconds on the Mac from a library selection (i.e. in the TV app, not in Finder). If the app discovers a broken link (i.e. files moved to a different Volume), then it will notice that on playback attempt, and ask you to repair the link by re-selecting the media file through a dialog box. It may automatically attempt to reestablish more broken links from the same base path.