Seen with Mining Dimension, Ore Creeper can spawn in an otherwise mob-less biome.
That makes the spawn rate absurdly high, since the spawn config is weight-based.
Could it be possible to have a data-driven spawn rule, by biome and/or dimension name/tag?

It just checks #minecraft:is_overworld and whether the spawn location is stone or deepslate. There is a tag called "is_mushroom" so I'll set it not to spawn there.

That would work thanks :D
Could it be possible to expose those value in a data instead of hardcoded?, it would allow for pack-specific fine-tuning, without the need for code change
maybe a tag for spawnable biome, spawnable block, and biome blacklist?
or maybe just spawnable biome, no blacklist, as a custom list, which could be expanded easily with a datapack or by mods for easy compat

Ah ok, I'm using the 1.21 Fabric version, and I didn't see any

In fact the spawn is not hardcoded in Forge and NeoForge. Since there it is done through json, so with a DataPack it can be changed. But I think it's a good idea to create a tag for the blocks.

If it is Fabric, as far as I know, it is only done through code. But with some Tags it should be solved.

I've added tags for the spawnable biome, the spawnable block, and a biome blacklist. With a datapack it will be easy to modify. Now by default it prevents spawning on Mushroom Islands.

Thank you very much, can't wait to try it :D