You didn't read the title wrong, you can create world templates, like the Tutorial world, just with resource packs in this mod.
That's why on this page I'll explain it with the world_templates.json file that comes in the mod by default to make it easier to understand

They are defined by the world_templates.json file in any namespace (directories in assets, like minecraft), having an override effect if you use the same namespace used by another resource pack, like the built-in the mod, which uses legacy, and an addition effect otherwise.

[
  {
    "buttonMessage": {"translate": "legacy.menu.play_tutorial"},
    "icon": "legacy:creation_list/tutorial",
    "templateLocation": "world_templates/tutorial.mcsave",
    "folderName": "Tutorial",
    "isGamePath": true,
    "downloadURI": "https://github.com/Wilyicaro/Legacy-Minecraft/raw/refs/heads/main/common/src/main/resources/assets/legacy/tutorial/tutorial.mcsave"
    "directJoin": true,
    "isLocked": false
  }
]

• buttonMessage -> the component used in the button message (mandatory)
• icon -> location of the button icon sprite, note that sprites are basically textures in the namespace:textures/gui/sprites directory (mandatory)
• templateLocation -> can be either a game path, that is, a path relative to the .minecraft, or a resource location, indicating the world file in .zip or .mcsave, which are the same format (mandatory)
• folderName -> name of the template world directory when created (mandatory)
• isGamePath -> if true, the templateLocation value will be used as a game path, otherwise as a resource location (it's false by default)
• downloadURI -> a URI that will be used to download the world file if it's a game path, and it supports a checksum to be more secure and allow updating the file when needed (optional)
• directJoin -> if true, ignores the Load Save screen and enters the world directly, as in the tutorial (it's false by default)
• isLocked -> if true, locks the Resource Assort selector, and hides the save seed, and it makes no difference if directJoin is true (it's true by default)