The workbench is more than just a code editor; it is a full suite of development tools:
Use Project > Create New Project to select a template or a blank project specifically for your target Arm core. iar-embedded-workbench-for-arm-8-32-1
If you are looking to test the environment before committing to a license, you can explore IAR's free trials which typically offer a 14-day full-featured evaluation. The workbench is more than just a code