It would be better if the user can have an option to choose the custom hold music as well under the IVR configuration settings, the same way we have under custom greetings for normal incoming calls.
Custom music could include uploading their own audio file or choosing from an audio bank
If you add your own hold IVR message, you can choose whatever song and upload it through there! We've used Murf.Ai to record our hold script, and underlayed music through Murf.Ai too