Are you able to share an example Flutter app which has Dicscourse embedded? As Sam mentioned, it’s not strictly supported, but if there’s anything easy we can do to fix/improve compatibility then we’re generally happy to do that.
The error in your screenshot could be related, but it doesn’t look like it’s coming directly from Discourse (we don’t have a ‘webcontent.js’ file). Most likely, it’s something being injected by your WebView.
It looks like Flutter webviews are backed by different OS engines, so this might be platform-specific.