Like many others i have the same problem.
My mac (Big Sur 11.5.1) and rekordbox 6.5.2 don't work together, and i get a warning that states "one or more files cannot be exported. Check the log file in "documents". In this document it only states title, artist, album and place for all of the songs that couldn't be exported
My USB 3.0 is in MS-DOT (FAT32) format and all my old songs have no trouble exporting. It is mostly new songs. I tried buy a song through itunes store for fun, and this song did get exported to the USB. It had a AAC format. So is there something with the software and the sound formats?