I still have original files in my computer.
The number of playlists are not too many, about 20 playlists. But songs (20k+) in the playlist is the problem.
Some of the playlists reference from other manually created playlists and use "Date added", "Plays" and "Rating" to create. These information won't exist after export playlists and songs then add them into a new library.
I called Apple Support, still waiting for their response.
Following image is one of the smart playlist with easy rules (Only "Rating"). I guess I can right click those "removed" songs and re-"Add to iCloud Music Library".
But songs in manually playlists vanished after "iCloud Music Library" is on. (The songs are still in the library, but not in the playlist.) I have no easy way to add them back into playlist.