I just tried to rename a file: Mandy Make Up Your Mind.mp3
To make the Up not uppercase (in keeping with norms of English), and I kept getting 'file already exists.' It took me a long time to figure out what the problem was. Apparently EXFAT -respects- case in filenames, but considers 'Up' and 'up' to be the same thing. The solution is to add a character as well as changing the 'U' to 'u,' like change the 'U' to 'ux', save it, then rename it again to delete the extra character. Knowing that EXFAT was designed by Microsoft this should not have surprised me. And I also discovered that it can't take '?' in a filename.