[Checkout.com] Cannot override final method Df\Payment\Method::acceptPayment() in vendor/magento2/checkout.com/Method.php

Extensions Checkout.com
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2

You are wrong: there is no acceptPayment method defined in the \Dfe\CheckoutCom\Method class in the latest 1.1.18 release.
An usual reason of such errors is ignorance or violation of the official installation and upgrading instructions.