Exactly what can I use in my asset package?

I’ve finished my asset package, but after reading the guidelines to submitting asset packages:

and asking the asset store team.

They say I could only use “primitive” things in unity in my asset package(I’m not sure what that means).
So does this mean I can’t even use a skybox in my example scene(which the material is imported from one of the unity packages).
And then I opened a new project just to check which components come with unity without importing anything and then I found out that basic things like “CharacterMotor”,“FpsInputController”, “Mouselook” and “CombineChildren” aren’t included?

Does this mean that I need to write those things myself just to be able to include a demo scene in my asset package?

No assets are included in a new project. A primitive refers to a built-in shape such as cube, sphere, etc. You can note that a standard package (CharacterController or whatever) is required for your asset to work.