This was marked as solved by Spotify staff. It's not solved after 3 years.  

Time for Spotify to catch up and offer at least Lossless CD level quality now like Tidal, Amazon Music, Qobuz do.  Spotify premium is compressed sounding.  

NOT SOLVED; 

https://community.spotify.com/t5/Accounts/Hi-fi-lossless-playback-FLAC-offer/td-p/1594628