That is a known issue - discovered long time ago and documented more than 2 years ago - the following topic is from September 2021.
TLDR:
sudo pacman -R openresolv
sudo systemctl enable --now systemd-resolved
sudo mv /etc/resolv.conf /etc/resolv.conf.bak
sudo ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf