Uninstall and reinstall the Display adapter
Instructions below.
https://windowstip.com/topic/i-cant-adjust-brightness-on-surface-go/
ALternatively:
-Run the latest Surface Pro update
- Alternatively, this is related to the power settings that the graphics card controls.
The issue is adaptive contrast which adjusts the screen depending on the color gamut of your current display (so if you shift from a dark mode web page to an all white web page, it will change the screen contrast, which would appear like brightness being dim slowly turning brighter).
- install Intel Graphics Command Center from the microsoft store
- find the POWER options under settings
- select power from the tabs on the top
- turn off display power savings