Onshape is a cloud-based, 3D CAD document system.
Onshape can export models in several formats supported by Sketchfab, including glTF, OBJ, STL, Collada, and IGES. We recommend glTF.
Right click your Part/Assembly and click Export... from the context menu. Or, click Export tab... from the Part tab menu.
Choose GLTF as the Format and any other options as needed. ( Details here ).
You can upload this glTF file directly to Sketchfab.
Then, you can adjust the camera, materials, etc. as needed.
Here's the result: