Where are playlists stored Samsung music?

Recently my Samsung Galaxy S9 upgraded to Android 10, and Google Play Music stopped showing album art (among the other problems like occasionally losing playlists), so I moved to Samsung Music. I've been using MusicBee for several years and several phones, but now when I try to sync the playlists/music, I'm having problems.

I'm trying to sync the music to the SD card, and I don't really care where the playlists go.

- Using the storage path SM-G960U1\Card\ with PLA, and sending the playlist to device, I get the error:
"Copy Failed - A device attached to the system is not functions. (Exception from HRESULT: 0x8007001F)"
for the playlist, and the SD card becomes unreachable until I disconnect/reconnect the phone.

- If I set the playlist type to M3U, I successfully get a playlist on the device. When accessed in MusicBee's device menu, I can play the list, and it shows me the music files in the location SM-G960U1\Card\Music\... The M3U file is in the Playlist directory on the SD card, as intended.

- The problem here is that the Samsung Music app detects the playlist, but not any of the music, so it shows up empty. If I open the playlist file, the music files are listed in \Music, without any reference to the SD card, so I assume it's looking in the phone main memory. Other older M3U files in that same directory (from previous versions of MusicBee?) have some sort of reference to the SD card, but not this one.

Thanks for any ideas. I would think this is a pretty common setup.

John S.