With the release of MapGen 1.12.0 the options for the map generator have gotten overhauled.
It was often the experience that people would use the sliders to try and customize the map generation. However this would often not generate maps as expected for players.
To try and help this situation the options have been reworked so that players can create custom map styles by selecting the terrain, biome, resource, and prop generators. (Edit) This is what previous generators were doing under the hood based on the slider options.
The options are for now available in the 2024.6.2-alpha-1 client version. In the meantime the old sliders do not work with the new map generator.