Unity Pro XL V11 is not compatible with Windows 11 or newer Windows 10 builds (21H2+). It may crash or fail to communicate with PLCs.
: The single license version of Unity Pro XL V11 is identified by part number UNYSPUEFUV1X Go to product viewer dialog for this item. .
Manually install .NET Framework 3.5 from Windows Features (Control Panel > Programs > Turn Windows features on/off).
Install Windows 7 on a VM (VMware or VirtualBox), then install your legit copy of Unity Pro XL V11. This isolates legacy software from your modern OS.