Smart Card Support
I connect to work computers using RDP and they require smart card authentication (Yubikey). This feature is essential for Gnome Connections to be an option for my use case.
Remmina supports sharing smartcards with RDP remote machines. See the screen shot below.
A side note: Flatpak currently doesn't have a way to use smart cards from flatpak applications. https://github.com/flatpak/flatpak/issues/3076