Many commands, such as Coil, Thicken/Offset, and Frame Generator, were moved to a modern UI panel framework for a more streamlined workflow.

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

Improvements were made to part modeling, assembly, and frame generator workflows to handle larger, more complex designs with less memory usage. Downloading for Free

The 2021 version brought significant enhancements to the underlying Inventor engine that powers OEM-based applications:

A long-requested Dark Theme was introduced to reduce eye strain.