Rick’s explanation is he has some friends at music labels who give him the original stems (isolated tracks) for educational purposes you can find the stems of

Rick’s explanation is he has some friends at music labels who give him the original stems (isolated tracks) for educational purposes you can find the stems of many songs online and some artists often offer remix packs (which you can easily obtain by contacting their label/publisher) you can also try splitting them yourselves with some ML: https://github.com/deezer/spleeter https://github.com/deezer/spleeter