On this Intel/Intel desktop rig I like to use…
sudo cpupower frequency-set -g performance
Otherwise, for conserving power on a laptop I might set…
sudo cpupower frequency-set -g powersave
But if you are getting…
Are you sure you have installed cpupower and enabled/started it in systemd?..
sudo pacman -S cpupower
sudo systemctl enable cpupower && sudo systemctl start cpupower