Images added using QStyleSheet becomes blur/aliased in PyQt5 Python

Question

I am using Qt5ct Version 5.11.3 on Raspberry Pi 4 (Debian Buster / Linux). I have used border-image in SetStyleSheet to add an image as the background of QPushButton from the resource file (.qrc converted to .py). The images become aliased and square edged as shown in the picture below.

The images I have used are of high DPI 4800x4800 pixels. I have also tried to reduce the pixels/DPI of images but they are still aliased. How can I make these background images look smoother. I am using 7-inch touch screen with 800x480 resolution.

Code for creating widgets/buttons :

self.pushButton = QtWidgets.QPushButton(self.centralwidget)
self.pushButton.setGeometry(QtCore.QRect(4, 130, 61, 61))
self.pushButton.setAutoFillBackground(False)
self.pushButton.setStyleSheet("background-color: gray;\n"
               "border-image: url(:/newPrefix/files (4)/hour_glass.png);")
self.pushButton.setText("")
self.pushButton.setFlat(False)
self.pushButton.setObjectName("pushButton")