The 720p that the service gives to PC and tablet seems to be not enough. Windows central and the verge have both learned that Microsoft is testing 1080p level video streaming to improve the experience of playing, especially for large screen players.
According to the verge
Xbox game streaming app for windows shows that Microsoft has added support for Xbox series x s in addition to the upgrade screen. In operation, the surface device is added to play as the game handle, and it can use the touch and gyroscope properties of the device.
It is not known when the new app will be launched, but there is news that Microsoft will hold games related activities in March. I believe they will take this opportunity to publish it.