I have a QDialog with QScrollArea, the QScrollArea has a QLabel containing pixmap. I need to draw on that pixmap. From what I have read in the documentation I should be able to draw directly to the pixmap since the pixmap inherits QPaintDevice. I was not able to do this. The paint event draws nothing and it "erases" the pixmap. What am I doing wrong?

import sys
import PySide6
from PySide6 import QtCore
from PySide6.QtCore import Qt
from PySide6 import QtWidgets
from PIL.ImageQt import ImageQt
from PySide6.QtGui import QPixmap, QPainter, QColor,QBitmap
from PySide6.QtWidgets import QDialog, QVBoxLayout, QLabel, QScrollArea


class MyQLabel(QLabel):
    def __init__(self,originalImage: ImageQt):
        super().__init__()
        self.originalImage = originalImage
        self.pixmap = QPixmap.fromImage(originalImage)
        self.setPixmap(self.pixmap)

    def paintEvent(self, arg__1: PySide6.QtGui.QPaintEvent) -> None:
        painter = QPainter(self.pixmap)
        rect = QtCore.QRect(QtCore.QPoint(0, 0), QtCore.QPoint(30, 30))
        painter.fillRect(rect, QColor("red"))


class MyScrollArea(QScrollArea):
    def __init__(self, originalImage: ImageQt):
        super().__init__()
        self.myQLabel = MyQLabel(originalImage)
        self.setWidget(self.myQLabel)


class MyQDialog(QDialog):
    def __init__(self, img):
        super().__init__()
        self.scrollArea = MyScrollArea(img)
        self.layout = QVBoxLayout()
        self.layout.addWidget(self.scrollArea, alignment=Qt.AlignCenter)
        self.setLayout(self.layout)


if __name__ == '__main__':
    app = QtWidgets.QApplication(sys.argv)
    image = ImageQt("img.png")
    imageViewer = MyQDialog(image)
    imageViewer.show()
    sys.exit(app.exec())