Before 1.18, "Single Biome" world generation of biome "The End" produces a fully end-stone-covered terrain, with the center (0,0) surrounded by obsidian pillars with end crystals. This is the correct situation.

Starting from 1.18 till 1.19, "Single Biome" of "The End" produces an overworld terrain but with only oceans and grass covered surfaces (some with stones underneath). This clearly is falsely generated.

Although this issue may be duplicate to some of the previous ones related to land generating in an ocean single-biome world (which was marked as "Working as Intended"), the generation of overworld blocks in "The End" biome is certainly faulty and unintended. This should be corrected.

(The screenshots are shot in 1.18.2, the same applies for the latest versions)

Screenshots 1 & 2 show how "The End" single biome generates overworld terrain

Screenshot 3 shows how "End Highlands" single biome generates overworld terrain without end stones, but also generates the end cities

Presumably, the game generates the structures correctly but the terrain wrongly.

Screenshot 4 shows when generating "Nether Waste" single biome, the ghasts also spawn normally, while the netherracks and the lava were replaced by grass blocks and water.

For all the "overworld terrain" mentioned above, there were (supposedly noise) caves and random mountains.

At last screenshot 5 was generated using "The Void" single biome, which was in fact quite funny.