It works :)

charts/apps/piped/templates/backend/lib/_container.tpl

@@ -16,7 +16,7 @@
     {{- if kindIs "string" . }}
     - {{ . }}
     {{- else }}
-    {{ toYaml . | nindent 4 }}
+    {{- toYaml . | nindent 4 }}
     {{- end }}
   {{- end }}
   {{- with .Values.backend.securityContext }}
@@ -48,7 +48,11 @@
         name: {{ include "backend.names.fullname" . }}
     {{- end }}
   {{- end }}
-  {{- include "backend.controller.probes" . | trim | nindent 2 }}
   ports:
   {{- include "backend.controller.ports" . | trim | nindent 4 }}
+  {{- with (include "backend.controller.volumeMounts" . | trim) }}
+  volumeMounts:
+    {{- nindent 4 . }}
+  {{- end }}
+  {{- include "backend.controller.probes" . | trim | nindent 2 }}
 {{- end -}}

charts/apps/piped/templates/backend/lib/_volumemounts.tpl

@@ -0,0 +1,60 @@
+{{/* Volumes included by the controller */}}
+{{- define "backend.controller.volumeMounts" -}}
+  {{- range $persistenceIndex, $persistenceItem := .Values.persistence }}
+    {{- if $persistenceItem.enabled -}}
+      {{- if kindIs "slice" $persistenceItem.subPath -}}
+        {{- if $persistenceItem.mountPath -}}
+          {{- fail (printf "Cannot use persistence.mountPath with a subPath list (%s)" $persistenceIndex) }}
+        {{- end -}}
+        {{- range $subPathIndex, $subPathItem := $persistenceItem.subPath }}
+- name: {{ $persistenceIndex }}
+  subPath: {{ required "subPaths as a list of maps require a path field" $subPathItem.path }}
+  mountPath: {{ required "subPaths as a list of maps require an explicit mountPath field" $subPathItem.mountPath }}
+          {{- with $subPathItem.readOnly }}
+  readOnly: {{ . }}
+          {{- end }}
+          {{- with $subPathItem.mountPropagation }}
+  mountPropagation: {{ . }}
+          {{- end }}
+        {{- end -}}
+      {{- else -}}
+        {{/* Set the default mountPath to /<name_of_the_peristence_item> */}}
+        {{- $mountPath := (printf "/%v" $persistenceIndex) -}}
+        {{- if eq "hostPath" (default "pvc" $persistenceItem.type) -}}
+          {{- $mountPath = $persistenceItem.hostPath -}}
+        {{- end -}}
+        {{/* Use the specified mountPath if provided */}}
+        {{- with $persistenceItem.mountPath -}}
+          {{- $mountPath = . -}}
+        {{- end }}
+        {{- if ne $mountPath "-" }}
+- name: {{ $persistenceIndex }}
+  mountPath: {{ $mountPath }}
+          {{- with $persistenceItem.subPath }}
+  subPath: {{ . }}
+          {{- end }}
+          {{- with $persistenceItem.readOnly }}
+  readOnly: {{ . }}
+          {{- end }}
+          {{- with $persistenceItem.mountPropagation }}
+  mountPropagation: {{ . }}
+          {{- end }}
+        {{- end }}
+      {{- end -}}
+    {{- end -}}
+  {{- end }}
+
+  {{- if eq .Values.controller.type "statefulset" }}
+    {{- range $index, $vct := .Values.volumeClaimTemplates }}
+- mountPath: {{ $vct.mountPath }}
+  name: {{ $vct.name }}
+      {{- if $vct.subPath }}
+  subPath: {{ $vct.subPath }}
+      {{- end }}
+    {{- end }}
+  {{- end }}
+- name: config-volume
+  mountPath: /app/config.properties
+  subPath: config.properties
+  readOnly: true
+{{- end -}}

charts/apps/piped/templates/backend/lib/_volumes.tpl

@@ -65,4 +65,7 @@ Volumes included by the controller.
   {{- end }}
 {{- end }}
 {{- end }}
+- name: config-volume
+  configMap:
+   name: {{ include "backend.names.fullname" . }}-config
 {{- end }}