Pure black materials will absorb all direct and indirect light. This is physically correct behavior. In real life, no naturally occurring material is completely black. For example, one of the darkest natural materials, coal, measures at “50, 50, 50” on an RGB luminosity scale.
Adjust your material color values to follow the physically based shading standards. In the Built-in Render Pipeline, you can use the Validate Albedo Scene View Draw Mode to determine whether Albedo values are PBR-compliant. You can use the Rendering Debugger in URP and HDRP to do the same.
Source: Unity Technologies Blog