As explained on the Windows Blog, Build 21332 sees the removal of the 3D Viewer and Paint 3D apps. Once the changes in this test build are applied to Windows 10 proper, it will mean the two apps ...

Now, how can you view a 3D model present in the .stp/ .step file on your Windows 10 PC? The native 3D apps like 3D Viewer or Paint 3D don’t let you open a STEP file.