Since you are searching for this information, you may have found out that there is no way for Vinagre remote desktop viewer to connect to a Windows Server via Windows Remote Desktop (RDP) when a RD Gateway Server is needed for the configuration.
What we did to make this work was only to install remmina on our machine using this command sudo dnf install -y remmina;.
Remmina by default supported the configuration using RD Gateway Server so we did not have to do nothing more than just use it.
Useful links:
- Vinagre is a remote desktop viewer for the GNOME desktop
https://wiki.gnome.org/Apps/Vinagre - Remmina is also a remote desktop client for GNU/Linux
http://www.remmina.org/
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