I run OPNsense as well as a few Linux systems with Webmin.
Webmin has an option to check for updates periodically and install them automatically (iirc this can be done for all updates, or just for the security-relevant ones). This ensures that the system is always up to date, or at least has all security fixes installed.
OPNsense, on the other hand, does not seem to have an option for that (correct me if I am wrong). However, if checking for updates and installing them can be done via the command line and without user input, it should be possible to run that as a cron job.
What command would I need to run for that? (Or is there an easier way?)
Btw, for a discussion of the pros and cons of automation, see https://security.stackexchange.com/q/183173/49551.