Webview net::ERR_FILE_NOT_FOUND

The problem happens when I want to load an Html page in WebView. It works fine on Qt 5.12. But in Qt 5.15 and Qt 5.14 I get this error: net::ERR_FILE_NOT_FOUND

The code:

WebView {
    anchors.fill: parent
    url: "file:///android_asset/index.html"
}

 I also tried with:

url: "assets:/index.html"

and I get net::ERR_UNKNOWN_URL_SCHEME