If you are using MeshStandardMaterial that is configured to be metallic - you must use an environment map / reflections map (docs.) Otherwise the material has nothing to reflect and just renders the reflections just black.
HDR / EXR are the most popular reflection (ie. IBL) map formats - you can find quite a ton of them online for free (Polyhaven, BlockadeLabs Skybox AI etc.) You load them similarly to the usual textures, but be sure to use the RGBELoader instead of TextureLoader. Then set the loaded texture to scene.environment (global, will be applied to all materials in the scene) or material.envMap (local, per-material.)