Orders in the Magento 2 admin area get stuck in a pending status. This happens for payment methods that require the shopper to be redirected to another web page.
Shoppers can abandon the checkout process at the redirected web page, meaning that it's impossible for the Magento 2 e-commerce to detect the abandonment. Adyen sends a notification when the payment offer is closed, but this needs to be enabled by Tech Support.
Search for the PSP Reference of a stuck order in the Offers tab in Customer Area (please ask firstname.lastname@example.org to enable this if you don’t see the 'offers' tab). If you see an offer closed or cancelled in the list, it means that the shopper abandoned the transaction before being redirected back to your e-commerce.
You can request Adyen support team to enable the OFFER_CLOSED notification via email@example.com, which will cancel these orders. This will not retroactively change the orders and to do so you must change the order in the database.
Other than that, offers will still stay open until they expire, which varies based on the payment method.