You can use polybar as well in Openbox. The standard panel in ArcoLinux is tint2 but you can replace this.

We edit the autostart file in folder ~/.config/openbox.

#tint2 &
sh ~/.config/polybar/ &

These lines came in with the update of the package : arcolinux-openbox-configs-git and it is saved in your /etc/skel. You need to copy/paste it to your home folder or compare differences with meld.

Log out and back in to see polybar at work.