What I expected to happen was...:
when i tried to generate a single biome world type relating to the nether like the crimson forest or warped forest it should generate those biomes

What actually happened was...:
but what happened was that it just generated a nothing relating to it other then what i can describe it as it looking like a really hot plain biome with nothing in it other then nether generated structures,

Notes

these generation for these nether biomes work exactly how they should in 1.16 to 1.17, but not 1.18

plus the 2 screenshots i added are worlds that i made as a single biome world in 1.16 and loaded them both in the snapshots of 1.19