Run it inside a Windows 10 (LTSC 2019) virtual machine (VMware or VirtualBox). Snapshot the VM before installing v21. When the emulator inevitably corrupts its RSLinx driver, you can roll back in 5 minutes instead of re-installing for 2 hours.
Version 21 was a transitional release where Rockwell Automation rebranded "RSLogix 5000" to "Studio 5000". The specific manual you likely need is the Getting Results Guide Rslogix Emulate 5000 V21l
RSLogix Emulate 5000 is a software application that acts as a "virtual PLC" (Programmable Logic Controller). It allows users to run Logix5000 controller projects on a standard Windows PC without the need for physical hardware (such as a ControlLogix or CompactLogix chassis, power supply, or processor). Run it inside a Windows 10 (LTSC 2019)
Version 21 is significant because it was the first release of the rebranded Studio 5000 environment Version 21 was a transitional release where Rockwell