With many workflows and procedures within Autodesk Inventor, there is often more than one method available to reach a given result. This characteristic also applies to file creation. As an alternative to the New command on the Quick Access Toolbar, you can access the file templates from the Application menu. You can also use the Quick Launch command in the Open dialog box.
Click
to expand the Application menu, then click the arrow next to New to expand the submenu.

Select Assembly to use the default template.

Notice that if you select New directly from the Application menu, the New File dialog box opens.
If you click the arrow next to New, the New submenu expands. Alternatively, the New submenu expands automatically after a short delay as you pause the cursor over the New parent menu.