Windows wrote: ↑
what is the correct in CentOS 8 ?
The systemd-sysv-install script is called by "systemctl enable/disable" when the given unit is a SysV init.d script. It needs to call the distribution's mechanism for enabling/disabling those, such as chkconfig, update-rc.d, or similar.
RHEL 6 had SysV and all services had init.d-scripts. RHEL 7 and 8 have systemd and most services have systemd unit files.
However, no systemd unit files have been created for all services, because those services are already deprecated and there is no point to put effort in them. They still have init.d-script. Systemd has some legacy support so that those services can still be used.
The "warning" is just a notification that network.service is a such case.