The “Discover more artists.” / “Fans also like.” / "Related artists" (the exact name varies depending on the version and client used) feature currently is accessible via individual artist pages.
The curated playlists were mostly recommended to me on the home page in the Spotify desktop client but I suppose you could find them by simply searching for "progressive metal" in that case as well.
Anyway, here are the playlist links if you're interested in those genre playlists specifically:
