Spotify had removed support for its Web Player for Safari on macOS towards the beginning of September 2017 due to security concerns relating to Widevine Digital Rights Management.
Spotify has quietly added back support for its web player for Safari on macOS as first spotted by wolkStroker on Reddit. Spotify has already updated its Web Player support Website with the mention of Safari in it and the feature is now available for use for Spotify users.
If you are unable to use Spotify on your Mac’s Safari, make sure to update Safari on the help section, or use private / incognito mode. You may also have to enable the web player if it’s displayed.