SUSE zypper update then patch?

I have a SUSE SLES15 SP2 system that needs patching / updating. I am not sure of the differences between updating the OS and patching the OS.

The way I have read it, updating - updates any rpms installed that it can. Patching applies SUSE security fixes. I am not sure if the zypper tool checks patches against package versions? if so would it not be best to update and then check for any patches ?

My question is; What is best practice here ? update or patch ? Or update and then patch ?