Back in 2017, when Google Pay was still called Android Pay, it integrated with PayPal competitor Visa Checkout. This allowed you to use data from Google's payment service anywhere Visa Checkout was supported. Last week, Visa announced that it's shutting down the service in 2020 and Google is removing support for it.
Visa aims to replace Checkout with an upcoming solution based on EMV SRC. It's supposed to be more robust and secure, but the shutdown can also be read as a capitulation to the all-encompassing PayPal. Mastercard offers a similar service called MasterPass, but although Google announced integration with the service back in 2016, the collaboration never came to fruition.
Of course, Visa credit and debit cards are still supported by Google Pay and aren't going anywhere. You simply won't be able to connect Google Pay and Checkout anymore, although you'd expect whatever the replacement is to be looked at again by Google if it manages to gain sufficient traction.