I found the issue in the settings of grafana
allow_embedding=true
then it works

Hi all
I want to embed a Grafana chart,
I tried two options:
-MMM-GrafanaChart
-MMM-iframe

In bothe cases this does not work. I get the message:
" Firefox may not open this embedded page. For your protection, 192.168.10.129 does not allow Firefox to display this page if it is embedded in another page. To display the page must be opened in a new tab."

in the developer tools I see
The “X-Frame-Options” directive “deny” prohibits the loading of “http://192.168.10.129:3000/d-solo/fdh9fixfg03y8c/msb-1og?orgId=1&panelId=1” in a frame.

How can I solve this. The MagicMirro is only internal, so the x-frame issue would’nt be an issue.
I’m using the server version of magicmirror