To fix weird shading in environment 3D models, focus on four key areas: normals, lighting, textures/UVs, and isolation testing.
Normals dictate how light hits surfaces—recalculate them to resolve "black faces" or uneven brightness from flipped/inconsistent data. Lighting issues (harsh directional lights, missing ambient occlusion) cause flat/splotchy shading—soften lights or add ambient occlusion. Ensure texture maps (normal/roughness) are applied correctly and UVs are distortion-free, as errors here create odd patterns.
If problems persist, simplify materials or use a basic test scene to narrow down whether the issue is with the model, materials, or lighting setup.