Noticed that there is a configuration file named “moss_patch_bonemeal.json” in vanilla worldgen datapack, placed in "worldgen/configured_feature". However, modifying this file does not change the spreading behaviour of moss block, but modifying “moss_patch.json” can change the moss patches generated in lush caves.
A datapack for testing is in attachment.
I also checked the code and confirmed that the spreading of moss block uses configured feature to generate moss patches.
//net.minecraft.world.level.block.MossBlock#performBonemeal
@Override
public void performBonemeal(ServerLevel serverLevel, Random random, BlockPos blockPos, BlockState blockState) {
CaveFeatures.MOSS_PATCH_BONEMEAL.place(serverLevel, serverLevel.getChunkSource().getGenerator(), random, blockPos.above());
}
Fixed in 22w44a.