The bug

The world creation screen lists "dungeons" as a possible structure which can be toggled on or off (despite it not actually affecting anything; see MC-77787). However, since 1.16 or so, the structure referenced here has not been called a "dungeon"; the game instead refers to these as "monster_room" in ID.

How to reproduce

1. Enter the world creation menu --> More World Options
2. Read the description under Generate Structures
3. Be in a world with the ability to execute commands
4. Use the /placefeature command, and type "dungeon", noting there are no results
5. Now type "monster_room" and execute it (underground next to a cave but inside a block should work, it's a tad tricky to get to work though)
6. Note that the structure placed by this is what is likely referred to as a dungeon instead

Expected results

Since the structure referred to in the option's description and given that specific namespaced ID are the same thing, their names would also match.

Actual results

One place refers to it as a "dungeon", whereas the other refers to it as a "monster room".

How to fix

Names should be changed; either the structure has its ID changed to "minecraft:dungeon", or the Generate Structures button refers to them as "monster rooms".