The welcome screen's toolbar has a search field. But it doesn't look like a search field. Typically search fields actually have a text edit frame with a blinking insertion point cursor. This one doesn't.
I am a bit puzzled by this one, some /computer/ show the border and some don't. Regardless of the theme or color scheme. I did not investigate. searchbox.qml has border.width: 1 border.color: Kirigami.Theme.textColor
Turns out this is a regression in Qt 5.12 From https://doc.qt.io/qt-5/qml-qtquick-controls2-textfield.html#background-prop > Note: If the background item has no explicit size specified, it automatically > follows the control's size. In most cases, there is no need to specify width or > height for a background item. This is currently not true with the Material theme on 5.12. The size was 0x0 until I set "height: search.height; width: search.width" on the background item.