itunes balance
What happens to my unused iTunes balance (credit) when iTunes no longer exists?
iMac, OS X 10.11
Question marked as
Nothing.
Your iTunes balance has no ties to the iTunes Application on a Mac. Its tied to your Apple ID which will be able to be used in the Music, TV and Podcasts Apps on macOS Catalina (if you choose to update) just like it can be used on multiple devices already.
If you do not update to macOS Catalina, then the iTunes application will not go away, and continue to work as it has.