World templates is an experimental feature, this feature will allow you to define templates that will be pasted into a newly created island/nether/hub. In order for this feature to work, simply copy your desired world save file into your game or server folder and rename it to something like island_template for island, nether_template for nether, and hub_template for hub. And specify it in the config file.

(Warning: This feature is available since 0.3.6+1.19.4 and heavily updated in 0.4.0+1.20.1.)