As far as I learned this feature is available (at least partially) for the desktop app. I cannot download that app at work, as downloads are blocked. A similar feature is not available for the webplayer. Spotify is well aware of this but it seems as if it sounds strange to them that ALL useres might like such a feature:
Currently the option to like/dislike songs in Discover Weekly is only available on the Spotify desktop app. If you think other users would also like this on the web-player, you can always submit it as an idea.
THIS is a quote from a comunity problem brought up to Spotify in 2017 and marked as solved (which should be true for the desktop app). So please, if you solve a problem, do it for all applications! Thank you!
Thanks for your feedback and suggestions on this one!
We're pleased to confirm that feedback buttons on Discover Weekly and Release Radar have now been added in the web player and you should see the option to “dislike” tracks or artists in those playlists.