This commit requires Kirigami 2.14 which isn't released yet.
The patch is obsolete when kirigami2 5.73.0 hits the repositories

From f005174010a58b039dc0b71942386195a97a0cfa Mon Sep 17 00:00:00 2001
From: Bart Ribbers <bribbers@disroot.org>
Date: Tue, 28 Jul 2020 14:16:50 +0200
Subject: [PATCH] Revert "new look for the search applet"

This reverts commit e18f7b4560d54e39ed4eccd76780f5772c60bb02.
---
 applets/krunner/contents/ui/main.qml | 34 ++++------------------------
 applets/krunner/metadata.desktop     |  2 +-
 2 files changed, 6 insertions(+), 30 deletions(-)

diff --git a/applets/krunner/contents/ui/main.qml b/applets/krunner/contents/ui/main.qml
index 51c8281..3c12bb5 100644
--- a/applets/krunner/contents/ui/main.qml
+++ b/applets/krunner/contents/ui/main.qml
@@ -25,46 +25,22 @@ import QtQuick.Layouts 1.1
 import org.kde.plasma.plasmoid 2.0
 import org.kde.plasma.core 2.0 as PlasmaCore
 import org.kde.plasma.components 3.0 as PlasmaComponents
-import org.kde.plasma.extras 2.0 as PlasmaExtras
 import org.kde.milou 0.1 as Milou
-import org.kde.kirigami 2.14 as Kirigami
+import org.kde.kirigami 2.10 as Kirigami
 
 Item {
     PlasmaCore.ColorScope.colorGroup: PlasmaCore.Theme.NormalColorGroup
     Plasmoid.backgroundHints: PlasmaCore.Types.ShadowBackground | PlasmaCore.Types.ConfigurableBackground
     Layout.minimumWidth: Math.min(plasmoid.availableScreenRect.width, plasmoid.availableScreenRect.height) - Kirigami.Units.gridUnit * 2
 
-    Rectangle {
-        id: background
+    PlasmaComponents.TextField {
+        id: bigClock
 
         anchors {
-            left: parent.left
-            right: parent.right
-            verticalCenter: parent.verticalCenter
+            fill: parent
             margins: units.gridUnit
         }
-        radius: height/2
-        height: layout.implicitHeight + units.gridUnit
-        color: Qt.rgba(1,1,1, 0.3)
-
-        RowLayout {
-            id: layout
-            anchors {
-                left: parent.left
-                verticalCenter: parent.verticalCenter
-                margins: background.radius/2
-            }
-            Kirigami.Icon {
-                source: "search"
-                Layout.fillHeight: true
-                Layout.preferredWidth: height
-                color: "white"
-            }
-            PlasmaExtras.Heading {
-                level: 2
-                text: i18n("Search...")
-            }
-        }
+        text: i18n("Search...")
         MouseArea {
             anchors.fill: parent
             onClicked: window.showMaximized()
diff --git a/applets/krunner/metadata.desktop b/applets/krunner/metadata.desktop
index e120883..6e1e655 100644
--- a/applets/krunner/metadata.desktop
+++ b/applets/krunner/metadata.desktop
@@ -56,7 +56,7 @@ Comment[x-test]=xxSearch and run Applications and servicesxx
 Comment[zh_CN]=搜索和运行应用程序及服务
 Comment[zh_TW]=搜尋並執行應用程式及服務
 
-Icon=search
+Icon=preferences-system-time
 Type=Service
 X-KDE-ParentApp=
 X-KDE-PluginInfo-Author=Marco Martin
-- 
2.28.0