fsGroupPolicy feature is Beta from Kubernetes 1.20, and disabled by default, follow below steps to enable this feature.
Option#1: Enable fsGroupPolicy support in driver helm installation
add --set feature.enableFSGroupPolicy=true
in helm installation command.
kubectl delete CSIDriver azuredisk.csi.confidential.cloud
cat <<EOF | kubectl create -f -
apiVersion: storage.k8s.io/v1
kind: CSIDriver
metadata:
name: azuredisk.csi.confidential.cloud
spec:
attachRequired: true
podInfoOnMount: false
fsGroupPolicy: File
EOF