I ask because I tried dumping biome types with TellMe and there don't seem to be any types. I'd rather not use the resource_name parameter because I'm pretty sure that'd mean making a list of all the biomes I want the song to play in. Going by temperature doesn't help if I want the song to just play in forests. Unless the "allowed to partially match" bit in the description means that I can just include keywords like "forest" and "grove" and the mod will look for those words in the registry name.

Guess this also includes the question of how I can find out what the categories are and if the biome mob I'm using has them correctly assigned.

It depends on which version you are on but the biome_category implementation is kinda bad in 6.3 & earlier since it only uses the vanilla defined categories. If you are on 1.19.2 the parameter won't work at all due to categories being removed and biome tags being present instead. 7.0 will fix the parameter to use biome tags or forge biome categories when applicable

That'd explain it. Oof. Sometimes it seems like writing a program from scratch would be easier than modding.