Encrypted syslog via TLS

If you are talking about the system logs, as far I know there is no option for that within the F5 configuration.

Anyway, the syslog-ng is not a F5 software, so you can configure the same way you configure in another Linux box.

Here is the official documentation for syslog-ng:

https://www.balabit.com/documents/syslog-ng-ose-latest-guides/en/syslog-ng-ose-guide-admin/html/procedure-configuring-tls-server.html