The new endeavouros-mirrorlist package version 1.4-1 needs manual intervention.
After system updates the new EndeavourOS mirrorlist is in file /etc/pacman.d/endeavouros-mirrorlist.pacnew. You need to copy that file onto /etc/pacman.d/endeavouros-mirrorlist.
So the following simple terminal commands need to be run:
cd /etc/pacman.d sudo cp endeavouros-mirrorlist.pacnew endeavouros-mirrorlist
This is needed as a preparation for future changes.
EDIT: as you can see below, this issue does not require any action by most users. Sorry guys, my bad!