GI1
You can read up on the Sensors permission here on the GOS website. Here is the full quote:
Sensors permission toggle
Sensors permission toggle: disallow access to all other sensors not covered by existing Android permissions (Camera, Microphone, Body Sensors, Activity Recognition) including an accelerometer, gyroscope, compass, barometer, thermometer and any other sensors present on a given device. When access is disabled, apps receive zeroed data when they check for sensor values and don't receive events. GrapheneOS creates an easy to disable notification when apps try to access sensors blocked by the permission being denied. This makes the feature more usable since users can tell if the app is trying to access this functionality.
To avoid breaking compatibility with Android apps, the added permission is enabled by default. When an app attempts to access sensors and receives zeroed data due to being denied, GrapheneOS creates a notification which can be easily disabled. The Sensors permission can be set to be disabled by default for user installed apps in Settings ➔ Privacy.