From Xojo Documentation
| This item was deprecated in version 2019r2.
Please use ComboBox.AllowFocusRing as a replacement.
If True, the control indicates that it has the focus with a ring around its border; if False, the appearance of the control does not change when it has the focus. At present, the focus ring appears only on macOS and Linux. On all platforms, the combobox gets a text insertion point when it has the focus. The default is True.
The following code turns off UseFocusRing.