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.
tableView->setSelectionBehavior(QAbstractItemView::SelectRows);
        tableView->setSelectionMode(QAbstractItemView::ContiguousSelection);
        tableView->setColumnWidth(RecentRequestsTableModel::Date, DATE_COLUMN_WIDTH);
        tableView->setColumnWidth(RecentRequestsTableModel::Label, LABEL_COLUMN_WIDTH);
        tableView->setColumnWidth(RecentRequestsTableModel::Amount, AMOUNT_MINIMUM_COLUMN_WIDTH);
        connect(tableView->selectionModel(),
            &QItemSelectionModel::selectionChanged, this,
            &ReceiveCoinsDialog::recentRequestsView_selectionChanged);
        
        columnResizingFixer = new GUIUtil::TableViewLastColumnResizingFixer(tableView, AMOUNT_MINIMUM_COLUMN_WIDTH, DATE_COLUMN_WIDTH, this);
        if (model->node().isAddressTypeSet()) {
            
            if (model->wallet().getDefaultAddressType() == OutputType::BECH32) {
                ui->useLegacyAddress->setCheckState(Qt::Unchecked);
            } else {
                ui->useLegacyAddress->setCheckState(Qt::Checked);
            }
        } else {
            
            ui->useLegacyAddress->setCheckState(Qt::Unchecked);
        }
        
        ui->receiveButton->setEnabled(model->canGetAddresses());
        
        connect(model, &WalletModel::canGetAddressesChanged, [this] {
            ui->receiveButton->setEnabled(model->canGetAddresses());
        });
    }
}
ReceiveCoinsDialog::~ReceiveCoinsDialog()