Keeping your Zimbra up-to-date by installing patches is essential for maintaining the security of your Zimbra servers. However patches are only available for supported (not end-of-life) versions. Recently the 8.8 versions of Zimbra went end-of-life and the Zimbra 9 versions are going end-of-life soon as well. Make sure all your Zimbra servers are on a supported version, more details on the Zimbra Lifecycle can be found at https://www.zimbra.com/product/product-lifecycle/.
It is equally important to install operating system security updates and have Zimbra run on (upstream) supported operating systems. If you are using CentOS, be advised that the EOL dates for CentOS 7 and CentOS8 Stream are closing in. More details can be found at: https://blog.centos.org/2023/04/end-dates-are-coming-for-centos-stream-8-and-centos-linux-7/
Please note that Zimbra EOL dates may not be in-line with operating system EOL dates.