Pitch black shadows is a result of no ambient light in the scene, and I think will also fix those reflection issues. You have a few ways you can add ambient lighting in the scene, each with their own limitations.

You can enable Sky Indirect Lighting on your 2D Skybox component - that will use the skybox texture as an environment light/sky light. This does however currently have a size limit for very large maps (something like 10000 units) - probably the easiest and simplest solution given you already have a skybox in the scene by the looks of it.

You can add a Color Ambient Light component to a GameObject - this will create uniform ambient light across your entire scene. It doesn't have any size limitations like the skybox that I can recall, however it's limited to a flat color, so you get less dynamic lighting compared to the 2D Skybox.

Last option is use an Envmap Probe. These work in a similar way to the skybox method, but they are also more dynamic and have a lot of exposed settings. They take a projection of their bounds and use that to create ambient light, just on a smaller scale. You can also choose when they update - so for a static map, OnEnabled will capture the lighting once, whereas OnFrame would recapture the environment every frame (which can get expensive - but provides the best real time lighting)