Hi there
If your seller central account is registered for Amazon Handmade, this means you are approved to list in the Handmade category and can decide to list in Handmade or the other categories if you so wish. You don’t need to apply again to sell on Amazon.
The one Amazon EU Seller Central account allows a seller to list their products across the various market places that include UK, FR, ES, IT, DE and recently NL (Netherlands)
There are different listing rules/fees depending on the category and some categories are ‘gated’ where you might need approval to list under. For more info see here

Only Handmade registered sellers can list under the handmade category.

You cannot list the same product in two separate/different categories.