Yes. You can control power settings on hard drives and even issue ATA commands to standby/sleep on demand. hdparm is a useful utility on Linux to accomplish this. From the hdparm man page:
hdparm provides a command line interface to various kernel interfaces supported by the Linux SATA/PATA/SAS "libata" subsystem and the older IDE driver subsystem....
Well, I would still set-up the (of course existing) netfilter firewall - if you are on a public network.
Namely, I would block any other traffic types like ICMP etc. Moreover, most port/system scanners detect system types by all kinds of error response ("port unreachable") etc, so you definitively decrease the attacking surface; your goal is to ...
Assuming RealVNC is not supported on the platform you are using (which is my case with arm64 Arch) I found the following solution.
As root, edit the config file in /root/.vnc/config.d/vncserver-x11
Insert the following at the bottom of the file
Restart RealVNC (or just reboot)