This is not a NoMachine problem but one created by the Arch repository.
You need to edit KGBUILD and set _autoservice=y and _autofirewall=n
### BUILD OPTIONS
# Set to y to enable nomachine service autostart
_autoservice=n
# Set to y to enable firewall autorules
_autofirewall=n
### END BUILD OPTIONS
You can also just set this:
sudo /etc/NX/nxserver --startmode nxd automatic
and set in /usr/NX/etc/server.cfg
EnableFirewallConfiguration 1
after installation.
Or better still, download and install manually from the NoMachine website:
wget https://www.nomachine.com/free/linux -O nomachine_current.tar.gz
sudo tar zxf nomachine_current.tar.gz -C /usr
sudo /usr/NX/nxserver --install redhat