Their devices dont have video cards so you cant use the hdmi for videos. It only allows you to create a "kiosk" for your machine. Youd have to have another device that uses the .local as its Jellyfin server.
Discussion
So a smart TV? If I'm understanding.
Or Apple TV , but basically you need a OS of some kind to run jellyfin or Plex to be connected to the media server which will be the Start9.
Roku?
You could technically add the http://iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjh44c7ead.local file to the jellyfin app on Roku, but I use cloudflare because it's easier to type a human readable domain.