For offline RSAT installation, you need to download the FoD ISO image for your Windows 10 build from your personal section on the Microsoft MSDN / Volume Licensing Service Center (VLSC). The image is called something like this: Windows 10 Features on Demand, version 1903.

Нужен преимущественно 1-й диск.

SW_DVD9_NTRL_Win_10_2004_64Bit_MultiLang_FOD_1_X22-21311.ISO
SW_DVD9_NTRL_Win_10_2004_64Bit_MultiLang_FOD_2_X22-21313.ISO

Установить RSAT на живую систему с диска

Get-WindowsCapability -Name RSAT* -Online |% {Add-WindowsCapability -online -name $_.name -source 'e:\'}

http://woshub.com/install-rsat-feature-windows-10-powershell
https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/features-on-demand-v2--capabilities