Thanks Dylan for the info. What is also important here: (1) The tracks in a local copy of a Tidal (or Qobuz) playlist are by default not in your library. Not even if you have favored all your tracks in all your Tidal playlists (in that case you will find the tracks under My Library > Tracks, but the versions there are not the ones that you find in your converted playlists). (2) There is already a six day old feature request related to this issue: Consistent and easy way to add a tag to a track (preferably while playing)