Here are two ways of showing charts in sitemaps.
First is rendering:
Image refresh=30000 url="http://10.4.28.237:3000/render/d-solo/ZkZGWpgRk/nilan-ind-ud-temperatur?refresh=30s&orgId=1&panelId=6&from=now-18h&to=now&width=1000&height=500"
Second using webview:
Webview url="http://10.4.28.237:3000/d/ZkZGWpgRk/nilan-ind-ud-temperatur?refresh=30s&orgId=1&tab=display&from=now-12h&to=now&panelId=6&fullscreen&kiosk=1" height=15
Both options works fine remote through the openhab android app, as well as myopenhab.org, on my system though, (beside rendering sucks and takes a huge amount of resources).
Btw… Grafana server us running on the same computer as openhab.