software.opensuse.org is an unreliable source that should be avoided as much as possible. Simply run sudo zypper in myrlyn cockpit from any terminal to have both ready to go. There’s no reason I’m aware of to have the Agama installer installed on an installed system, unless possibly you are an Agama developer.
No. It is installed when one selects KDE and is not installed when one selects GNOME or Xfce, because it is pulled in by the x11 (strictly speaking, by the x11_enhanced) pattern and these patterns are not part of the default Wayland-only GNOME/Xfce.