Hi, Paul.
The page that @Jim_F shared is the right place to start with Roon. That page will clarify that you can use your phone to control Roon but you also need to deploy a “Roon Core” in your home.
I gave you some advice on how to get a Roon display on your TV using an Apple TV. I mistakenly assumed that you already had Roon running. Until you have Roon deployed, my advice doesn’t apply. I wanted to clarify this so that you don’t have the expectation that you can just buy and use that Apple TV app and get the experience I showed you in the photo I shared. Before you can use that TV app, you’d need to get a complete Roon setup up and running.
Good luck with all of this! It can be complicated stuff. But even if you choose to not run Roon, there’s a lot you can do with the A/V setup you’ve got (TV, sound bar, satellites, KEFs). Hope you have fun and enjoy your system! Sorry for any confusion I caused.