NVIDIA Blog:
GeForce NOW makes gaming more convenient by letting members link their gaming accounts directly to the cloud service. Starting Aug. 22, such support extends to Xbox accounts — alongside existing support for Epic Games and Ubisoft automatic sign-in — enabling seamless access across devices.
After linking their Xbox profiles just once, members will be signed in automatically across their devices for all future GeForce NOW sessions — speeding access to their favorite PC games, from Fallout 76 to Starfield to Forza Horizon 5.
This new feature joins Xbox game library sync on GeForce NOW, which allows members to sync their supported Xbox Game Pass and Microsoft Store games to their cloud streaming library. Members will enjoy a more unified gaming experience with the ability to instantly play over 140 Xbox Game Pass titles across devices.
Source:

At Gamescom 2024, GeForce NOW Brings ‘Black Myth: Wukong’ and ‘FINAL FANTASY XVI Demo’ to the Cloud
GeForce NOW announces 'Black Myth: Wukong', 'FINAL FANTASY XVI Demo' available today, and Xbox automatic sign-in at Gamescom 2024.
blogs.nvidia.com