The default location for music in Big Sur is ~/Music/Music/Media where ~ is your user's home folder. You can use Music > Preferences > Files to check that this is the path being used. You can use File > Library > Organize Library > Consolidate File to copy in any file that is outside the designated media folder into it. Once done you should be able to remove the old ../iTunes/iTunes Media/Music folder without affecting your Music library. There is always a possibility however that you might have some songs in iTunes Media that haven't been added to Music, so you might want to give the folder a cursory scan before you remove it completely, or back it up elsewhere first.
A similar approach should be used with the TV app and any content you have in ../iTunes/iTunes Media/Movies and ../iTunes/iTunes Media/TV. You might also have audiobooks or podcasts, etc. in the old iTunes Media folder that you want to check are imported to their respective apps before you discard the old iTunes Media folder.
tt2