Spotlight2D

[amap1380]

It can be achieved with regular Light2D but it needs custom sprites which are inflexible and can't be changed.
With a Spotlight2D node its much easier to do custom lighting like line of sight and etc.

[eon-s]

Godot 4 has a PointLight2D node, maybe it can just get a from and to angles to restrict the region and work as a 2D spotlight.

[Calinou]

With GradientTexture2D and its 3.x backport, you can already do this using a Light2D and a GradientTexture2D. You'll need Godot 3.5beta1 or 4.0alpha for this, as GradientTexture2D is not available in Godot 3.4.x.