As I advised you should search for the CVE in the errata search, so for CVE-2021-31618 this would be Security and bugfix errata for Univention Corporate Server
As you can see, the vulnerability was fixed with errata 5.0-0.45 for UCS 5 and errata 4.4-8.1008 for UCS 4.
Nessus indicates that it only checked the package version number:
So the vulnerability was patched and there is no need to update the package as the version number does not indicate the patch level.