Yes, that is because it is installed with the defaults and we don’t install discover or any graphical paclage managers.
As for the default GUI package manager, please read this:
If you want a GUI package manager, there are 3 options for you to choose from. All are in the AUR. pamac-aur, octopi and bauh
But you shouldn’t. Discover uses packagekit and packagekit has no support for manual intervention. Using any packagekit-based solution on an Arch-based distro is a good way to break your install.
Of course, you can still do that on EndeavourOS by installing discover and packagekit-qt5