"No WebView plug-in found!" when using QtWebView Qt-5.12 on RHEL 8.8

Question

I have to create gui to display pdf files. For this I am using QtWebView class. Th requirement is to use Qt-5.12 version for this.

In the pro file:

QT += qml quick webview

In the qml file:

import QtWebView 1.1
...

WebView {
        id: webView
        anchors.fill: parent
        url: "https://www.qt.io"
        onLoadingChanged: {
            if (loadRequest.errorString)
                console.error(loadRequest.errorString);
        }
    }

In the main.cpp I have added

QtWebView::initialize() 
QGuiApplication app(argc, argv);

When I run the code it starts with warning "No WebView plug-in found!"

Any idea why this is happening?