Using master (98958c81f5065a5de13699d46995d278ecb6709e) with Qt `5.12.3` (also tested with depends) with multiple wallets available. None are shown in the `Open Wallet ->` menu in the gui. The wallets can be loaded from the console, bitcoin-cli etc.
connect(backupWalletAction, &QAction::triggered, walletFrame, &WalletFrame::backupWallet);
        connect(changePassphraseAction, &QAction::triggered, walletFrame, &WalletFrame::changePassphrase);
        connect(signMessageAction, &QAction::triggered, [this]{ showNormalIfMinimized(); });
        connect(signMessageAction, &QAction::triggered, [this]{ gotoSignMessageTab(); });
        connect(verifyMessageAction, &QAction::triggered, [this]{ showNormalIfMinimized(); });
        connect(verifyMessageAction, &QAction::triggered, [this]{ gotoVerifyMessageTab(); });
        connect(usedSendingAddressesAction, &QAction::triggered, walletFrame, &WalletFrame::usedSendingAddresses);
        connect(usedReceivingAddressesAction, &QAction::triggered, walletFrame, &WalletFrame::usedReceivingAddresses);
        connect(openAction, &QAction::triggered, this, &BitcoinGUI::openClicked);
        connect(m_open_wallet_action->menu(), &QMenu::aboutToShow, [this] {
            m_open_wallet_action->menu()->clear();
            std::vector<std::string> available_wallets = m_wallet_controller->getWalletsAvailableToOpen();
            std::vector<std::string> wallets = m_node.listWalletDir();
            for (const auto& path : wallets) {
                QString name = path.empty() ? QString("["+tr("default wallet")+"]") : QString::fromStdString(path);
                QAction* action = m_open_wallet_action->menu()->addAction(name);
                if (std::find(available_wallets.begin(), available_wallets.end(), path) == available_wallets.end()) {
                    
                    action->setEnabled(false);
                    continue;
                }
                connect(action, &QAction::triggered, [this, name, path] {
                    OpenWalletActivity* activity = m_wallet_controller->openWallet(path);
                    QProgressDialog* dialog = new QProgressDialog(this);
                    dialog->setLabelText(tr("Opening Wallet <b>%1</b>...").arg(name.toHtmlEscaped()));
                    dialog->setRange(0, 0);
                    dialog->setCancelButton(nullptr);
                    dialog->setWindowModality(Qt::ApplicationModal);
                    dialog->show();
                    connect(activity, &OpenWalletActivity::message, this, [this] (QMessageBox::Icon icon, QString text) {