Haven’t tried charts, but I just tried to implement a weather widget from this thread:
https://community.openhab.org/t/use-webview-and-iframes-to-show-a-pretty-weather-forecast/16068
It works locally and on my.openhab but no luck on the iOS app. Searching it seems like this is a known issue with webviews but bug reports have been closed but I’m not sure why.