Music.xml file loading time

Hello,

i have Catalina and on MacOS the music app. I export the music file "music.xml" from the music app and then i link rekordbox to this file. 

After that i choose iTunes in the rekordbox-tree and the songs are listed.. but if i close rekordbox and start it again, i have to import all the "iTunes" tracks again... so.. this looks too much time... what i am doing wrong ?

hope someone could help me,

thanks,

roman