I definitely have the playlists show up when logged into the same account on the web client and FinAmp:
The playlists exist as .m3u files in the top folder of my music collection and the ones that work with Jellyfin use relative paths.
EDIT: Seems to be similar to this issue, Imported playlists into Jellyfin can't be read
But I can’t even get the playlists to even show up.