Interesting…this stuff is complicated for the end user…I can see why Apple ecosystem is successful, although I am not part of it for many reasons.
My m3u format is this:
Classical New Age Piano Music - Canon In D Pachelbel.mp3
Geek Music - Interstellar Theme (4 min version) (Hans Zimmer Cover).mp3
George Winston - Carol of the Bells.mp3
George Winston - Thanksgiving.mp3
Hania Rani - Eden.mp3
But Symphonium does not recognize this format when trying to import
Then provide logs for that operation and be sure there’s those files in the same folder as the playlist.
And this is only complicated because you do not use a media server but raw access.
Most proper servers like OpenSubsonic ones or Jellfin/Emby, Plex have APIs to access the playlists natively.