The current style does not support customization of this control

I've a qml code which executes fine when build in QT 6.0.4 but prompt me a runtime error when i build it using QT 6.5.1.

The complete error is the following:

QML Rectangle: The current style does not support customization of this control (property: "background" item: QQuickRectangle(0x22c49ddefc0, parent=0x0, geometry=0,0 100x40)). Please customize a non-native style (such as Basic, Fusion, Material, etc)

Below is the portion of code in which the background style is present.

Button {
    id: listen_btn
    text: "Press Me"
    font.pixelSize: 18
    background: Rectangle {
        implicitWidth: 100
        implicitHeight: 40
        border.width: 1
    }

This warning is about attempting to customize native style.

Have a look here: QTBUG-109438

This is what the attached change comment says. Take a look at the last paragraph to fix your issue QT_QUICK_CONTROLS_IGNORE_CUSTOMIZATION_WARNINGS, but as the comment says "customize native styles on your own risk".

> Warn users when they customize native styles
>
> Since Qt 6, the default style is no longer the Basic style, but
> instead depends on the platform the application is run on. In
> addition, the introduction of the native styles (which are not
> designed to be customized) means that users customizing controls can
> run into visual issues and not understand why.
>
> This patch partially addresses this issue by warning when a native
> control is customized (i.e. a delegate is overridden):
>
> "qrc:/main.qml:11:22: QML QQuickItem: The current style does not
> support customization of this control (property: "contentItem" item:
> QQuickItem(0x1637375d210, parent=0x0, geometry=0,0 0x0)). Please
> customize a non-native style (such as Basic, Fusion, Material, etc).
> For more information, see:
> https://doc.qt.io/qt-6/qtquickcontrols2-customize.html#customization-reference"
>
>...
>
> [ChangeLog][Important Behavior Changes] Customization of native styles
> will now result in warnings. Non-native styles (such as Basic) should
> be used for customization purposes, or a custom style. If you are
> aware of the risks and still want to customize these controls, you can
> ignore the warnings by setting
> QT_QUICK_CONTROLS_IGNORE_CUSTOMIZATION_WARNINGS to 1.

In order to pick a different control style than the default one, there are multiple options depending on your use case. Have a look at the documentation Using styles in QtQuick Controls.

The simplest would be to use import QtQuick.Controls.Basic.