New Mac Won't Play Purchased Movies From Library On Apple TV App

When I attempt to play any of the films in my library of purchased content, the window for the movie opens for only a split second then disappears, leaving me unable to play the files.

• Verify that you were signed in to the Apple TV app, through the app’s Account menu, using the matching Apple Account as used for the purchases. Authorization would cover that already, but please verify.
• Consider keeping a copy, but remove one downloaded media files from the library. Then for purchased movies, stream directly from Apple’s servers (no download), or download a fresh copy. If that behaves differently (working), then do the same for other films as well.
• As a test, for files in .mov/.mp4/.m4v container (not HLS/.movpkg), try playback in QuickTime Player.

Brand new Mac …

Buyers would get 90 days special support, to help you get going and get the most out of your new device. Make use of that, especially for initial hiccups. That is what it is for.

Apple Complimentary Support - Official Apple Support

Contact Apple for support and service - Apple Support

error -54

That error is about file/folder permissions. Migration Assistant may have done something that isn’t supported anymore on the new OS, especially if the version gap is significantly large.

What was the old macOS version?

Is the new macOS version Sequoia 15.1?

Try creating a new TV app Library, and importing your media files into that. Try a few files first, just to verify that it works, before importing all the files that you want there.