Superflat worlds cannot be created without using presets

The Bug

If you create a super flat world in this version, you will get a message that the data pack cannot be loaded and the world will not appear in the world list.

This does not happen if you go to the "Presets" screen and select any preset from the list (including "Classic Flat").

Game output

19:18:10.297
Error reading worldgen settings after loading data packs: Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:villages]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_plains]=cwq@13cdfd26}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_desert]=cwq@fff33b4}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_savanna]=cwq@36810c06}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_snowy]=cwq@4151d8a3}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_taiga]=cwq@b068ddf}, weight=1]], placement=dgd[spacing=34, separation=8, spreadType=LINEAR, salt=10387312, locateOffset=hg{x=0, y=0, z=0}]]} is not valid in current registry set; Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:strongholds]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:stronghold]=cwq@7aaec50e}, weight=1]], placement=dgc[distance=32, spread=3, count=128]]} is not valid in current registry set
19:18:10.297
Failed to load datapacks, can't proceed with server load
java.util.concurrent.ExecutionException: java.lang.RuntimeException: Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:villages]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_plains]=cwq@13cdfd26}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_desert]=cwq@fff33b4}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_savanna]=cwq@36810c06}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_snowy]=cwq@4151d8a3}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_taiga]=cwq@b068ddf}, weight=1]], placement=dgd[spacing=34, separation=8, spreadType=LINEAR, salt=10387312, locateOffset=hg{x=0, y=0, z=0}]]} is not valid in current registry set; Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:strongholds]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:stronghold]=cwq@7aaec50e}, weight=1]], placement=dgc[distance=32, spread=3, count=128]]} is not valid in current registry set
	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)
	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)
	at dyq.a(SourceFile:2124)
	at dyq.a(SourceFile:1972)
	at dyq.a(SourceFile:1941)
	at ehm.A(SourceFile:286)
	at ehm.b(SourceFile:230)
	at ead.c(SourceFile:40)
	at dzx.a(SourceFile:16)
	at eab.a(SourceFile:121)
	at eba.a(SourceFile:27)
	at dyr.b(SourceFile:94)
	at edu.a(SourceFile:492)
	at dyr.a(SourceFile:94)
	at dyr.c(SourceFile:165)
	at auy.execute(SourceFile:103)
	at dyr.b(SourceFile:165)
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
	at org.lwjgl.system.JNI.invokeV(Native Method)
	at org.lwjgl.glfw.GLFW.glfwWaitEventsTimeout(GLFW.java:3174)
	at com.mojang.blaze3d.systems.RenderSystem.limitDisplayFPS(SourceFile:222)
	at dyq.f(SourceFile:1150)
	at dyq.e(SourceFile:737)
	at net.minecraft.client.main.Main.main(SourceFile:236)
Caused by: java.lang.RuntimeException: Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:villages]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_plains]=cwq@13cdfd26}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_desert]=cwq@fff33b4}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_savanna]=cwq@36810c06}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_snowy]=cwq@4151d8a3}, weight=1], a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:village_taiga]=cwq@b068ddf}, weight=1]], placement=dgd[spacing=34, separation=8, spreadType=LINEAR, salt=10387312, locateOffset=hg{x=0, y=0, z=0}]]} is not valid in current registry set; Element Reference{ResourceKey[minecraft:worldgen/structure_set / minecraft:strongholds]=dfo[structures=[a[structure=Reference{ResourceKey[minecraft:worldgen/configured_structure_feature / minecraft:stronghold]=cwq@7aaec50e}, weight=1]], placement=dgc[distance=32, spread=3, count=128]]} is not valid in current registry set
	at com.mojang.serialization.DataResult.lambda$getOrThrow$4(DataResult.java:100)
	at com.mojang.datafixers.util.Either$Right.map(Either.java:99)
	at com.mojang.serialization.DataResult.getOrThrow(DataResult.java:93)
	at dyq.a(SourceFile:1952)
	at zj.a(SourceFile:40)
	at dyq.a(SourceFile:2122)
	... 21 more

How To Reproduce

1. Create a new world (World options -> Click once on world type -> Create a new world)

2. Observe that an error message is displayed (The safe mode button does not work at all)

Workaround

Go to the "Presets" screen, select "Classic Flat", and then choose "Use Preset". Then the world generates as normal.