From the image that you’ve posted on that thread, you can’t chroot because you didn’t mount correctly:
mount /dev/sda1 /mnt
You’ve got an error because you should run mount commands as root:
sudo mount /dev/sda1 /mnt
Take note that arch wiki (and many tutorials) use $ as first character to indicate commands that can be run with “normal” user and # for commands that should be run as root.
This can be run with normal user;
$ systemctl status firewalld
This one should be run as root:
# mount /dev/sda1 /mnt
For chroot-ing, it’s easier to run first sudo su, so all the next commands will be executed as root.