For the 1.20.1 - 9.2.2 version there's no battle music playing for trainer or wild. I was redirected by a support mod on Discord to post it here, who has also confirmed on their end that the battle music was not working for them either.
To spare a few back-and-forth posts, my music settings are maxed out, I did two fresh reinstalls, one using Forge and the other using CurseForge to no avail. I also know this is a new occurrence because I used to play 1.16.5 several months ago, and I can confidently say that the battle music worked back then. All the other sounds such as cries, sound effects, ambient & menu music are currently working. Pokemon Center Music is not working either, though this is the one thing I remember not working even back in 1.16.5.
If there's something I'm doing wrong on my end, or a value I need to tweak, please help me in the proper steps as to how to fix this issue, and if this is an actual bug please sticky it in Discord so others can also see it.