I see you tagged your post as using the ‘Amazon Music Unlimited’ music service - That service should show the playlist and it normally allows the user to select any track to begin playback from a playlist. Are you using the installed service from within the Sonos App? If so, could you perhaps be selecting a Station, rather than a playlist?
A screenshot is attached from my AM service within the Sonos App.. it shows a playlist called ‘Pop Hits’.. just chosen here at random.
However if you are using the Amazon Music ‘Native’ App and sending the music to Sonos using either ‘direct control’, or perhaps ‘Apple AirPlay’, then you currently need to select the track you wish to play, or switch to, in the Amazon App.
HTH