It was noticed that discover has high CPU use even when idle.

I narrowed this down to a Kirigami.LoadingPlaceholder and furtder to the QQC2 ProgressBar.

Breeze has its own animation engine for progress bars, which calls updateItem regularly even for invisible items.

Reproducer:

import QtQuick 2.15
import QtQuick.Controls 2.15

ProgressBar {
        id: p
        width: 100
        height: 100
        visible: true
        onVisibleChanged: console.log(this, visible)
        indeterminate: true

        Timer {
                interval: 1000
                repeat: false
                running: true
                onTriggered: parent.visible = false;
        }
}

Run with QT_LOGGING_RULES=*.debug=true to see the scheduled draws.

Originally reproduced downstream: http://bugzilla.opensuse.org/show_bug.cgi?id=1210747