[2023] So I thought that by ticking the Creative box when creating a custom world would turn off the survival aspects of the world...

Note this has been changed in beta to be more in line with what you would expect. Creative is now a difficulty. Difficulty settings are also fully moddable

The custom world button will be removed, it shouldn’t still be there on beta.

You can make custom worlds still but they must be as an actual new world mod.