If you look at the values.yaml of the IKO's Helm chart you'll find:
useIrisFsGroup: false
Let's break down what it is and in what situations you may want to set it to true.
FsGroup refers to the file system group.
InterSystems IRIS is a Complete Data Platform
InterSystems IRIS gives you everything you need to capture, share, understand, and act upon your organization’s most valuable asset – your data.
As a complete platform, InterSystems IRIS eliminates the need to integrate multiple development technologies. Applications require less code, fewer system resources, and less maintenance.