Theme Mode Extension & Hiding creating options in admin panel

Can you please tell me is this for client work (where only an admin can see the option panel) or for redistributing as a standalone theme?

In any case, if it’s for client work, then the solution you linked to is the correct one. You’ll still have the plugin installed and an admin can still make changes to the structure if needed.

If you want to include it for redistributing in a theme, then you’ll need to strip our the API (inside wordpress-creation-kit-api) and initialize all the custom fields and post types directly inside your theme’s code.