I dont get why metal materials are appearing black (using Metal/Rough workflow in both UE/Painter)

If you already have some sort of ambient specular source in the scene(SkyLight, Reflection Actors…), then it’s down to your textures and/or material.

Your metals need to have a Base Color value above 180 sRGB and they need to have pure white in the Metalness. Also make sure your RMA or individual Roughness/Metalness/AO textures have sRGB disabled to ignore gamma correction.