In Spotify I can find an artist and create a radio of it. This is not possible since Volumio?
Nope, however, this feature is in the future roadmap. The new Spotify Web API supports the capability to generate playlists based upon artists, albums and tracks. So in principle, it should be fairly easy to create a Spotify Artist Radio feature.
To do this we need to enable Volumio users to authenticate with their Spotify accounts instead of just plugging their usernames and passwords into the plugin. After that, we’ll be in a position to add Artist/album/track radio playlists.
Hopefully by early summer we can have something working here. In the meantime, the Spotify Connect plugin works great and you can get Spotify Artist Radio that way.