iTunes library to Music App on Big Sur upgrade

I recently upgraded to Big Sur after being reluctant to lose iTunes. I had tens of thousands of songs in my iTunes library that have been built up over 18 years. All songs were rated and with play counts and all this information seems to be gone on the Music app. Also songs that I have remixed myself haven't transferred across and all my playlists are gone. Hundreds and hundreds of them. Years of work. Is this normal? Can I fix this?

Devastated :(