søren20,
Thank you for reaching out at Apple Support Communities today. If I understand correctly, you’re experiencing issue where some of your display has a shadowy, or darker, area than expected. It looks like this may be in the same place regardless of what is displaying on the screen, but you notice it more when it’s a uniform lighter color. Does this sound right?
If it’s not always in the same area, is it possible that the issue is related to image persistence?
Avoiding image persistence on Apple displays - Apple Support
If not, have you tried any troubleshooting to see if you can resolve it? Things like restarting, testing in safe mode and in a new user to see if it persists, and logging into macOS Recovery to access Safari from there will help you narrow it down between a software and hardware issue on your MacBook Pro.
How to use safe mode on your Mac - Apple Support
Set up users, guests, and groups on Mac - Apple Support
About macOS Recovery - Apple Support
Cheers.