While ending the contract is on Apple’s initiative, Goldman Sachs wanted out reasonably soon after the service started. Goldman Sachs has been losing billions on its services primarily due to the daft conditions that Jobs’ Mob has insisted that its services provide.
For example, Goldman Sachs wanted Apple fanboys to go through a credit check and apply for the card, but Apple said no. This has meant that many cards went to fanboys who could not pay the bank back. Apple Card users pay less often than credit card users from other banks.
Apple wanted Card customers to receive their bills on the same day (banks typically try to spread these bills out to avoid a deluge of customer service calls). Goldman Sachs blames Apple for regulatory issues that Goldman has had with the Consumer Financial Protection Bureau and the Federal Reserve over the card.
Apple seems to have found someone else to play banks -- Synchrony Financial and American Express have been named. Citigroup decided not to back the Apple Card in 2019 due to (well-founded) concerns that it wouldn't earn the company any money.