What type of layer acts like a transparent sheet of glass allowing effects to be applied to all layers below it?

An adjustment layer serves as a transparent sheet that enables the application of effects to all layers located beneath it in the timeline. When you create an adjustment layer, any effects added to it will impact all layers below without altering the individual properties of those layers. This feature is particularly useful for applying color correction, blurs, or any other effects globally to a composition, making it easier to maintain a cohesive look without having to apply each effect individually to every layer.

In contrast, a null layer functions primarily as a control layer or parent without visual properties and does not directly apply effects. A solid layer is used to create backgrounds or elements with specific colors, while a shape layer is used to construct vector shapes for illustrations or graphics. None of these options have the capability to serve as a universal effect layer across multiple underlying layers in the same way that an adjustment layer does.