If you are building a package that needs to go on an iso it is good practice – if technically possible – to build it in a clean chroot environment.
It is like having a small Arch Linux computer system on your ArcoLinux. A kind of jail Arch Linux they call it on the wiki.
So we start on the wiki.
I will not copy/paste over any text but rather ask you read that page and follow that page.
We will follow it together and in the end we will have a building script to get a better workflow next time.
arch-nspawn $CHROOT/root pacman -Syu
makechrootpkg -c -r $CHROOT