According to this doc: https://docs.adyen.com/developers/marketpay/marketpay-overview
Supported countries (12)
MarketPay is currently available for the following countries: Austria, Belgium, Finland, France, Germany, Ireland, Italy, the Netherlands, Portugal, Spain, the United Kingdom (including Isle of Man & Jersey), and the United States.
According to this: https://www.adyen.com/our-solution/online-payments/marketplaces
Payout 25+ countries
Which is correct and where can I see the list?
The difference here is what MarketPay supports vs the functionality of paying-out.
MarketPay includes functionality like KYC/Customer verification, funds management, as well as payout. This set of functionality is currently available in the 12 countries mentioned in the MarketPay documentation overview.
For the payout to 25+ countries, this is referencing the functionality of paying out to a bank account or card, independent of the MarketPay solution. This is represented in the docs under the third party payouts documentation