iTunes to Big Sur/Music = lost songs

In November I upgraded from Mojave to Big Sur. Everything seems fine except for my music library. The number of songs available to me in Music is about one tenth the size of my iTunes library; in fact it appears that the only music that made the transition is the stuff I purchased from the iTunes Music Store. The library used by iTunes is still on my 2014 MacBookPro, so Is there a way to "re-do" the iTunes to Music transition?

Edit: Also, none of my playlists came over in the transition. I would like to get those back too.