[KevinH]

If it was being blocked by our URLInterceptor you would see the following in qDebug:

        // otherwise block it to prevent access to any outside Sigil user file path
        info.block(true);
        qDebug() << "Warning: URLInterceptor blocking access to url " << destination;
        qDebug() << "    from " << info.firstPartyUrl();
        return;

So if you are not seeing that Warning then QtWebEngine itself is blocking that url not anything we are doing. My guess is missing a restart after changing that setting is the issue.