The following code can be runned using qmlscene and displays some text followed by an emoji.

import QtQuick 2.12

Item {
    width: 300
    height: 100

    Text {
        anchors.centerIn: parent

        font.pixelSize: 30
        text: "Here is a bug: \u{1f41e}"
    }
}

When the code is runned with QT_SCALE_FACTOR set to an integer value, such as 1, 2, 3 (e.g. env QT_SCALE_FACTOR=2 qmlscene bug.qml), the emoji is displayed correctly.

But when QT_SCALE_FACTOR is set to a non-integer value, such as 1.5 (e.g. env QT_SCALE_FACTOR=1.5 qmlscene bug.qml), the emoji is displayed at a wrong place, in bad quality and has a wrong size.

Also, if i run qmlscene with --textrendertype native, then all text is drawn at a wrong place, in bad quality and has a wrong size.

I can reproduce this on Linux and on Android (did not test on other platforms), but only with Qt Quick applications. Qt Widgets applications seem to be not affected.