Sorry if this is obvious or has already been discussed…
In the Tidal app, start an artist or track Radio. Tap on the queue list symbol in the player controls. Tap the three dots in the upper right of the queue list. Tap ‘add to playlist’ from the popup menu. Tap ‘create new playlist’, give it a name and save.
In Roon, go to settings, services, Tidal, and tap ‘sync now’. When the sync finishes, your new Tidal Radio playlist appears in your Roon playlists and Bob’s your uncle.
But TIDAL’s radio isn’t that great for my user case in particular. I decided to try several stations just now and it’s just too limited for my tastes. It plays a lot of the same artists and albums, for a 50 song playlist it should pick from a wider variety of material.
Although I suppose it depends on what you’re playing and wanting to get out of it, for some people that’s probably what they prefer. I personally lean towards discovery of new indie music, and want the station to be different each time, so for me TIDAL radio isn’t very good at all. Google Play Music has a really nice variety on their stations for indie music, so I basically do the same steps you described with GPM, then use Soundiiz to convert the playlists to TIDAL, then play them in Roon. I do the same thing with Spotify’s awesome curated playlists. It’s a great time for music lovers with all the options we have!