Java Edition:False Map Feature Tag
Beta 1.8 added the map feature tag, which allows the player to choose if they want structures to generate or not. When you update to Beta 1.8, this tag needs to be added to your world, and consequently set to 1. However, if you update to Beta 1.8 Pre-release (pre-reupload or reupload), it will add the world features tag, but set it to 0. The only way to avoid this is to skip Beta 1.8 Pre-release, and go straight to Beta 1.8 Pre-release 2 ;) or later. This will add the world features tag, though will set it to 1. This can be also reset through level.dat regeneration, which is a type of World Save Insertion.
This discontinued feature is exclusive with many other normal Minecraft items/mobs, including some other discontinued features. This is due to the unfortunate fact that this prevents structures other than dungeons and desert wells from generating.[1]
Unobtainable
It is impossible for these items or mobs to be present in a world with this discontinued feature:
Items:
• Elytra
• Shulker Shell
• Shulker Box & 16 colors of them
• Pigstep Music Disc
• Pig Snout Banner Pattern
• Pig Snout Banner
• Dragon Head
• Gilded Blackstone
• Heart of the Sea
• Conduit
Mobs:
• Piglin Brute
• Many Persistent, Non-named Mobs
Discontinued Features:
• Certain Overstacked Items
• Any Item From Above
• Totem of Undying
• Axeless Vindicator
• Piglin Armor
• block.minecraft.illager_banner
• Searge Book
• Negative Durability Boots *except iron **obtainable with downgrading
• Orders Book
Partially Obtainable
These features are possible in some versions with no structures but not all of them.