[KevinH]

FWIW, Mac has long included and used the certifi module and in the PluginRunner Dialog we explicitly set its path in this snippet. Should we be doing the same for Windows 10 (and 11)?

#ifdef Q_OS_MAC
    // On Mac OS X, it appears that QProcess does not inherit the callers process environment at all
    // which directly contradicts the Qt documentation.
    // So we simply read the system environment and set it for QProcess manually
    // so that python getpreferredencoding() and stdout/stderr/stdin encodings to get properly set
    if (settings.useBundledInterp()) {
         // determine path to site-packages/certifi/cacert.pem to set SSL_CERT_FILE
         QDir exedir(QCoreApplication::applicationDirPath());
         exedir.cdUp();
         QString cert_path = exedir.absolutePath() + PYTHON_SITE_PACKAGES + "/certifi/cacert.pem";
         env.insert("SSL_CERT_FILE", cert_path);
         env.insert("QT_PLUGIN_PATH", QDir(QCoreApplication::applicationDirPath() + "/../PlugIns").absolutePath());
         env.insert("QT_QPA_PLATFORM_PLUGIN_PATH", QDir(QCoreApplication::applicationDirPath() + "/../PlugIns/platforms").absolutePath());
    }

Since the Windows build of Sigil also includes the python certifi module in its Python site-packages, perhaps just creating an SSL_CERT_FILE environment variable and setting its value to point to the right file will be enough to fix everything (even for the current Windows 10 build of Sigil 2.7.0).