Importing files to Apple TV app on MacOS

Dear all,

I'd like to import media to my Apple TV application on my Mac mini from the very same computer by doing following:

1. Open up the Apple TV app
2. Chose "Importing Files"
3. I select a .mkv file from my Downloads folder (on Mac HD)
4. Nothing happens.. The dialog windows close itself as if the selection was successful but no items visible in the Apple TV app.

This was my first try ever to add files to the app, so I suspecting maybe some of my default settings are not ok.

Thanks in advance for any hint!

BR, Peter.