Hi !
Endeavour didn’t provide discover ootb. If you want to using it, the package is in the repo.
sudo pacman -S discover packagekit-qt5
Please take not that its not recommended to using it for updating the system, since he can soft-lock pacman. Personally i’m using it only for kde modules and Flatpak. For that you need to upgrade your system before (you can also pick the good one but the first option is easier).