If you want take your Starfield experience to next level you can enable Gyro aiming on the ROG Ally by using the Handheld Companion app.
How To Setup Gyro On The ROG Ally
Install Handheld Companion on your ROG Ally, you can follow my guide here.
Setup your quick tools window hotkey in the Hotkeys section. I have mine as left on the d-pad + A but you can put whatever you want.
Now press that quick tools window hotkey you just created. A menu should pop up on the bottom right of your screen. You can press LB and RB to move through the tabs. Move over to the third tab and scroll down to Motion control settings.
Configure your Motion control settings like I have on my screen. Output device is Right Stick and Style of input should be Joystick Camera.
Motion activation can be set to Enabled (Turn off with a button) which means Gyro is always on unless you hold the hotkey. Disabled (Turn on with buttons) means you hold the hotkey while playing to use the gyro. I play with Disabled and I set mine to the Left Trigger. So when I hold the Left Trigger button while playing it will activate the motion settings.
You also adjust the deadzone and sensitivity as well.
Minimize Handheld Companion and launch Starfield.
Once the game launches and you’re in the game, press and hold the Gyro hotkey and swing your ROG Ally around.
With the latest Patreon build they also finally implemented some gyroscope/joystick weight logic. This allows the user to define how and when gyro can take over a moving joystick input. It should be available to the public within a week or so. You can join the Patreon here if you want the update earlier.