Many commands, such as Coil, Thicken/Offset, and Frame Generator, were moved to a modern UI panel framework for a more streamlined workflow.
The 2021 version brought significant enhancements to the underlying Inventor engine that powers OEM-based applications: AutoDesk Inventor OEM 2021 Free Download
A long-requested Dark Theme was introduced to reduce eye strain. Many commands, such as Coil, Thicken/Offset, and Frame
Access to Inventor OEM 2021 is generally restricted because it is a commercial development platform rather than a standard consumer product. Inventor OEM - Autodesk Platform Services such as Coil