In the last couple of months, Google Pay has undergone a tremendous amount of transformation, both in terms of its looks and function. Google merged the international Pay app with its Indian counterpart (formerly called Tez) following the latter’s Flutter rewrite and it even got a new logo quite recently. But unlike most other Google services, the new GPay has so far lacked a proper dark mode, but that's finally making its way to the beta version of the app.
Google Pay India showed signs of an upcoming dark mode with a tweaked splash screen back in September, but the main app interface itself kept its glaring white layout. With the latest beta, GPay has picked up a more complete dark mode implementation that works across the board.
The app settings, however, don’t have a toggle to trigger the mode manually; it will automatically follow your device theme setting. Google may introduce a manual option at some point in the future, like many of its other apps have, but it sticks to the automatic mode right now.
The new dark theme is rolling out with GPay beta version 119.1.4, although it's still not available widely for those enrolled in the beta program through the Play Store. You can instead grab the app from APK Mirror to get the new theme sooner.