To list all available desktop environments in Gentoo, you can use the following command to view the installed packages and their descriptions related to desktop environments:

emerge -pv | grep "^\[ebuild" | grep "desktop environment"

This command filters through the ebuilds (Gentoo's way of packaging software) to find those that are related to a desktop environment. Here is an example output, which will list various desktop environments available in Gentoo:

[ebuild   R    ] media-libs/cogl-1.20.0::gentoo ~amd64  -gnome -kde -qt5 -X -wayland -x11-base
[ebuild   R    ] x11-apps/xclock-1.0.7::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libXcomposite-0.4.5::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libXdamage-1.1.5::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libXfixes-5.0.3::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libXrandr-1.5.2::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libxcb-1.13.1::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libxkbfile-1.0.9::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-libs/libxkbcommon-0.8.2::gentoo ~amd64  -Xorg -wayland
[ebuild   R    ] x11-libs/libxshmfence-1.3::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-terms/xterm-324c::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-wm/metacity-3.2.5::gentoo ~amd64  -gnome -kde -qt5 -X -wayland -x11-base
[ebuild   R    ] gnome-extra/gnome-backgrounds-3.28.0::gentoo ~amd64  -gnome
[ebuild   R    ] media-libs/libepoxy-1.5.3::gentoo ~amd64  -Xorg -wayland
[ebuild   R    ] x11-apps/xterm-290::gentoo ~amd64  -Xorg
[ebuild   R    ] x11-wm/compiz-bc578a3c_git::gentoo ~amd64  -gnome -kde -qt5 -X -wayland -x11-base
[ebuild   R    ] kde-plasma/plasma-desktop-5.20.5::gentoo ~amd64  -kde
[ebuild   R    ] x11-wm/openbox-3.6.1::gentoo ~amd64  -Xorg
[ebuild   R    ] kde-frameworks/kwayland-

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