i guess the title already describes it pretty good. I don't know if this is a problem on your side or on the beneath's so sorry if I reported it to the wrong authors.

Have you got a link to that mod?

https://mods.curse.com/mc-mods/minecraft/254629-the-beneath

https://github.com/Shinoow/The-Beneath/blob/master/src/main/java/com/shinoow/beneath/common/world/WorldProviderDeepDank.java#L58

I have a feeling its their issue as they are returning false on isSurfaceWorld Unless im missing a way to know if I should spawn ores (Feel free to correct me)