Your favorite stations are located under RADIO -> YOUR STATIONS -> Your favorites.
This view shows a summary of your RADIO activity: it shows your favorite stations and the stations you have recently listened to.
Your favorites were automatically taken over when the app was updated from version 4 to 5. Login with a user account is no longer possible from version 5. If your favorites are not displayed after the update, you could try restarting the app. Otherwise you would have to search and mark them again. If you have a radio.net user account, you can use it to log in to the radio.net website www.radio.net and view your favorites there.
Furthermore, the song marker function has been removed from the app, as it was unfortunately not used enough. If you have a radio.net user account, you can log in to the radio.net website and view your favorites there and open them on iTunes, Amazon and YouTube.