Actually both are same there is no difference in results, multiphysics includes mechanical with electro magnetic tool bar, mechanical is purely mechanical tool bar the difference I have added and shown in images but there will be no difference in results

  1. Step 1:

    Opening in multiphysics environment

  2. Step 2:

    options available in multiphysics

  3. Step 3:

    Opening in mechanical environment

  4. Step 4:

    options available in mechanical