Install the official plugin. Then also keep MeshLab or Microsoft’s 3D Builder (free) for STL repair. For power users, Solid Inspector (paid) pairs well to validate imported STLs as solids.
, it is not a mesh repair or editing tool. Think of it as a translator , not a surgeon. If your STL is flawed or huge, you still need external software. The plugin’s biggest failure is not warning users about this limitation upfront. sketchup stl import plugin