@ZoomerGirl Try steps one and five in this guide:
https://www.tenforums.com/tutorials/70157-enable-disable-adaptive-brightness-windows-10-a.html
For step five, your graphics driver is old enough that it may not have all the listed options. While it's generally not necessary to update a driver that's working fine, in this case, it's worth doing if nothing else helps. You can get the newest driver from Intel for your processor and graphics chip here:
https://www.intel.com/content/www/us/en/products/sku/85212/intel-core-i55200u-processor-3m-cache-up-to-2-70-ghz/downloads.html
Run the installer as an admin: right-click on the download and select "Run as administrator." Restart your computer afterwards and before trying to play.
It's possible that the newer driver will handle screen brightness properly on its own, so if you prefer, you can start by installing the driver and test that before changing any other settings. Either way is fine.