Try hardcoding the group, since that's the group in the external Conduit image.

charts/conduit/Chart.yaml

@@ -2,5 +2,5 @@ apiVersion: v2
 name: conduit
 description: Conduit is a simple, fast and reliable chat server powered by Matrix.
 type: application
-version: 0.2.7
+version: 0.2.8
 appVersion: "0.6.0"

charts/conduit/templates/deployment.yaml

@@ -33,10 +33,9 @@ spec:
       {{- end }}
       serviceAccountName: {{ include "conduit.serviceAccountName" . }}
       securityContext:
-        {{- if .Values.persistence.enabled }}
+        # the conduit group is 1000 in the image
+        # set fsGroup to allow write to PVC
         fsGroup: 1000
-        {{- end }}
-        {{- toYaml .Values.podSecurityContext | nindent 8 }}
       containers:
         - name: {{ .Chart.Name }}
           securityContext:

charts/conduit/values.yaml

@@ -42,9 +42,6 @@ conduit:
 podLabels: {}
 podAnnotations: {}
 
-podSecurityContext: {}
-  # fsGroup: 2000
-
 securityContext: {}
   # capabilities:
   #   drop: