OK, I now unfortunately have new problems.
Online install doesn’t work (my previous installation was offline) - when the installer gets to 13%, it just hangs there.
That seems to be a mirror issue, according to this thread: Installation stuck at 13% - #17 by Deadlyhydra
So I ran “sudo pacman -Syy archlinux-keyring”, then updated the mirrors (“Update Mirrors EndeavourOS” button in the Welcome screen, not the Arch mirror buttons), and everything seemed to be going fine at first, but the installer broke at 5%, just as it was preparing the partition – the window suddenly just closed with no message. I tried running the installer again, same result.
So now I’m stuck on how to solve that and successfully run the online installer.