The blackening of the gusset plate is generally caused by two reasons:

1. Insufficient light, supplementary lights are needed. It is recommended to add supplementary lights from the new rendering interface, and check double-sided lighting, which can illuminate the ceiling;

2. Overlapping of gusset plates. Press Ctrl+2 to enter the wireframe mode. If there are black shadows flashing on the gusset plates, it means overlapping. Delete the overlapping parts, reset the starting point, and then cover it again.