[Add-on] We can't add any biomes and features at all

I can't add any biomes and features with addon even if I use same seed and same addon(same json).
In 1.16.40, they can be added but in beta, they can't.
Of course I made sure "creation of custom biomes" is 'true'.
If it is not a bug, please tell me in detail what's changed about adding biomes and features by recent update to beta.