I used the user_pkglist option on EndeavourOS installer installing Cosmic alone not on top of other Desktop.

Run this before starting Installer on the liveSession of EndavourOS ISO (from a terminal):

following with adding packages list:

With cosmic-greeter (greetd):

wget -qN --show-progress -O /home/liveuser/user_pkglist.txt https://raw.githubusercontent.com/EndeavourOS-Community-Editions/cosmic/main/user_pkglist.txt

And to change systemd services module to enable cosmic-greeter:

sudo wget -qN --show-progress -O /etc/calamares/modules/services-systemd.conf https://raw.githubusercontent.com/EndeavourOS-Community-Editions/cosmic/main/services-systemd.conf

Using SDDM as Login Manager (DM):

wget -qN --show-progress -O /home/liveuser/user_pkglist.txt https://raw.githubusercontent.com/EndeavourOS-Community-Editions/cosmic/main/user_pkglist-sddm.txt

you have to edit /home/liveuser/user_pkglist.txt and uncomment the needed vulkan-driver for your GPU (Driver) (or virtual machine)

And make sure to install online choosing no-desktop !

If GDM is used it comes with a minimal GNOME session so --- On first boot change session to cosmic:

and enjoy tinkering: