When I tried to install VEEAM 11 on a Windows 7 x64 VM, it couldn’t install Microsoft PowerShell v5.1. The reason is very simple, it needs Windows Update service enabled and a working internet connection.
In my case, the Windows Update Service was disabled.
It may be possible to install it offline by downloading Windows Management Framework 5.1.
After enabling and starting Windows Update service, the installation of VEEAM will continue as expected. A reboot will be necessary and we are good to go.