The generation for the Basalt Deltas, Warped Forest, and Crimson Forest biomes in the Nether for version 20w45a seems to be bugged. Neither the Warped or Crimson Forests spawn with huge fungus trees, meanwhile, they continue to have Weeping and Twisted vines along with patches of Nether and Warped Wart.
As for the Basalt Deltas, none of the large, jagged terrain formations, lava pockets, or sinkholes are spawning.

Steps to reproduce:

• Load a (recommended Creative Mode) world in snapshot 20w45a
• Enter the Nether
• Find a Warped Forest, Crimson Forest, or Basalt Deltas biome (/locatebiome is recommended)

Expected result: Generation would be normal, huge fungi and/or spiky terrain

Actual result: Terrain is flat, no huge fungi and/or spiky terrain is to be found

Screenshot 1: 20w64a
Screenshot 2: 1.16.4
Same seed, same coordinates, world created in different versions (6801919674075935891 seed, 747 70 -17 coordinates)