In a WSUS environment it might be necessary to change a value in the registry to get access online and install the tools:
HKLM/Software/Policies/Microsoft/Windows/WindowsUpdate/AU/UseWUServer to 0 and restart windows update service.
Via Powershell with administrative rights you can install the tools with the command:
Get-WindowsCapability -Name RSAT* -Online | Add-WindowsCapability -Online
References:
https://www.reddit.com/r/sysadmin/comments/9l2sa5/rsat_on_windows_10_1809/
https://www.virtualizationhowto.com/2019/07/download-windows-10-1809-1903-rsat-install-using-new-windows-fod/
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