it works

chart/templates/logging/loki/values.yaml

@@ -24,7 +24,7 @@ monitoring:
 {{- if (eq .Values.loki.strategy "scalable") }}
   serviceMonitor:
     enabled: {{ .Values.monitoring.enabled }}
-    {{- if .Values.istio.enabled }}
+    {{- if and .Values.istio.enabled (eq (dig "istio" "mtls" "mode" "STRICT" .Values.loki.values) "STRICT") }}
     scheme: https
     tlsConfig:
       caFile: /etc/prom-certs/root-cert.pem