How to render a local HTML file?

I have an HTML file in my Download folder: /mnt/sdcard/Download/file.html
Brave browser renders this HTML file if I use this URL:
`file://mnt/sdcard/Download/file.html`

Bur your plugin flutter_webview_plugin cannot render it, I get the error ERR_ACCESS_DENIED.

1. How to render a local HTML file with your plugin (if it is possible) ?
2. If not possible, which other WebView plugin can render a local HTML file ?
3. What is the built-in Flutter WebView class ?

Does this error message mean: my flutter app is not allowed to access my Download folder, because my device is not rooted?

Thanks in advance and regards

Device: GALAXY S8+ SM-G955F. Android 8.0. Not Rooted
Flutter beta v0.5.1. Dart 2.0.0-dev.58.0. Windows 10