I see that `legacy` means `P2PKH` in both command line options and RPC help info:
```
-addresstype
What type of addresses to use ("legacy", "p2sh-segwit", or "bech32", default: "p2sh-segwit") 
```
```
getnewaddress ( "label" "address_type" )
...
2. address_type    (string, optional, default=set by -addresstype) The address type to use. Options are "legacy", "p2sh-segwit", and "bech32".
...
```

The useLegacyAddress checkbox describes itself as “Generate legacy address” - however, it actually makes the wallet GUI generate “p2sh-segwit” address for the user if it's checked.
{
    if(!model || !model->getOptionsModel() || !model->getAddressTableModel() || !model->getRecentRequestsTableModel())
        return;
    QString address;
    QString label = ui->reqLabel->text();
    
    OutputType address_type;
    if (!ui->useLegacyAddress->isChecked()) {
        address_type = OutputType::BECH32;
    } else {
        address_type = model->wallet().getDefaultAddressType();
        if (address_type == OutputType::BECH32) {
            address_type = OutputType::P2SH_SEGWIT;
        }
    }
    address = model->getAddressTableModel()->addRow(AddressTableModel::Receive, label, "", address_type);
    SendCoinsRecipient info(address, label,
        ui->reqAmount->value(), ui->reqMessage->text());
    ReceiveRequestDialog *dialog = new ReceiveRequestDialog(this);
    dialog->setAttribute(Qt::WA_DeleteOnClose);
    dialog->setModel(model);
    dialog->setInfo(info);
    dialog->show();
    clear();
    
    model->getRecentRequestsTableModel()->addNewRequest(info);
}
void ReceiveCoinsDialog::on_recentRequestsView_doubleClicked(const QModelIndex &index)