Hi @oandroido,
To add on to what Marco said, if you are seeing a lens flare that looks like this, rather than overall screen brightness:
there are two things I can think of that could be causing it. First, check in your World Outliner. If you see an actor called “PostProcessVolume” in the level, that is likely what’s causing the effect. You can either delete the volume, or adjust/disable the lens flare settings in the details panel of the Post Process Volume.
If there is no Post Process Volume in the scene, it’s possible that it’s set in your project settings. Even without Post Processing in the scene, projects allow for several post processing effects to be applied in the project settings, which would effect all cameras and scenes in the project.
Open the project settings (Edit/Project Settings) and search for “Lens”. You’ll see a setting called “Lens Flares (Image based)” in the Engine/Rendering settings. If that option is checked, be sure to disable it.
-Alex