I’m Helen from Shopify Support. Welcome to the Community, and thanks for reaching out about this.
Fortunately, stores based in Spain are eligible to use Shopify Payments, which is why you are not seeing a third party integration with Stripe. Shopify Payments is the main payment gateway offering in your region, and is recommended due to a number of benefits in using it over a third party gateway. Benefits such as:
Setting up your Shopify Payments account is quick and easy, and you’re immediately able to accept major debit and credit cards in your checkout. For more information on this and the specific account requirements for your region, please see the Help Doc on Setting up Shopify Payments.
All that being said, is there a particular reason why you are wanting to use your own Stripe account to accept payments on your store?