Since a 1.16 snapshot, bamboo jungles don't generate in Default worlds.

(And no, the new custom world generation isn't at fault; this bug occurred in 20w14~, because the /debugdim command did not generate files for bamboo jungle or bamboo jungle hills.)

Cause:

In net.minecraft.world.level.biome.OverworldBiomeSource.class, the List has all overworld biomes listed, except for Bamboo Jungle and Bamboo Jungle Hills.