Viewport vignette effect?!?

Hey guys! The background is just a plane. Both the swords and the background plane have an unlit, mono-color material.
I don’t have any post process volumes in the scene, for the rest, I’ve used the default empty project Unreal offers. I also deactivated auto-exposure.
I have no idea what that is, but I noticed that this kind of radial vignette effect is here by default in Unreal!