https://retroshare.cc/downloads.html
https://www.flathub.org/apps/details/cc.retroshare.retroshare-gui
    ! 0.6.6
https://download.opensuse.org/repositories/network:/retroshare/AppImage/

https://build.opensuse.org/project/show/network:retroshare
    https://build.opensuse.org/project/repository_state/network:retroshare/xUbuntu_21.10

    1 source /etc/os-release
    #2 wget -qO - https://download.opensuse.org/repositories/network:/retroshare/xUbuntu_${VERSION_ID}/Release.key | sudo apt-key add -
    #3 sudo sh -c "echo 'deb https://download.opensuse.org/repositories/network:/retroshare/xUbuntu_${VERSION_ID}/ /' > /etc/apt/sources.list.d/retroshare_OBS.list"

Then install RetroShare with:

    #1 sudo apt-get update
    #2 sudo apt-get install retroshare-gui