How to use proxy + change UserAgent in PyQt5?

Question

PyQt

I have an implemented connection to a proxy and, accordingly, the request itself:

def exec_func(ip, port, user, password):
    QNetworkProxy.setApplicationProxy(
        QNetworkProxy(
            QNetworkProxy.HttpProxy, 
            hostName=ip,
            port=port,
            user=user,
            password=password

        )
    )
    app = QApplication(sys.argv) 
    web = QWebView()
    web.show()
    web.load(QUrl("https://t.me"))
    app.exec_()

However, when I include a user-agent change:

class MyBrowser(QWebPage):
    def userAgentForUrl(self, url):
        return "Mozilla/5.0 (Windows NT 6.2; WOW64) AppleWebKit/537.15 (KHTML, like Gecko) Chrome/24.0.1295.0 Safari/537.15"

class Browser(QWebView):
    def __init__(self):
        QWebView.__init__(self)
        self.setPage(MyBrowser())
def exec_func(ip, port, user, password):
    QNetworkProxy.setApplicationProxy(
        QNetworkProxy(
            QNetworkProxy.HttpProxy, 
            hostName=ip,
            port=port,
            user=user,
            password=password

        )
    )
    app = QApplication(sys.argv) 
    web = Browser()
    web.show()
    web.load(QUrl("https://t.me/"))
    app.exec_()

Then everything stops working, all kinds of page loading errors occur:
Protocol "tg" is unknown (QtNetwork Error 301)
Host unreachable (QtNetwork Error 99)
Or does not load the page at all and shows a black screen. Does anyone know what this could be related to?