class QAcccessibilityEdit(QLineEdit):
def focusInEvent(self, QFocusEvent):
self.setStyleSheet("background-color: " + GlobaleEinstellungen.aktbedienelementhintergrundfarbe)

...
self.editsuchen = QAcccessibilityEdit(self)
self.editersetzen = QAcccessibilityEdit(self)

You already have a custom class, so now just use it in your code.

One note, do note use name starting with Q, it will only confuse people working on that code thinking it's an official Qt class until they find your custom declaration.

findChildren

thank you, that's what I want.

The two solutions of @SGaist I don't understand or I have no idea how to realize it.
perhaps he can make a codeexample.

thank you. but my problem is, how get I a list of all Components of the type QLineEdit.

To answer this directly, if I understand you correctly: win.findChildren(QLineEdit) will return a list of all QLineEdits in your MainWindow, if that's what you want. However, either of the two solutions suggested by @SGaist would be better than writing code to go through each QLineEdit doing something.

class QAcccessibilityEdit(QLineEdit):
    def focusInEvent(self, QFocusEvent):
        self.setStyleSheet("background-color: " + GlobaleEinstellungen.aktbedienelementhintergrundfarbe)

...

self.editsuchen = QAcccessibilityEdit(self)
self.editersetzen = QAcccessibilityEdit(self)

I hope that is the correct answer for your question

class MainWindow(QMainWindow):
    def __init__(self):
        # Konstruktor von QMainWindow aufrufen
        super().__init__()

        self.setWindowTitle("Marlems barrierefreier PQT-Texteditor")
        self.setMinimumSize(QSize(900, 370))
        self.setWindowIcon(QIcon("PQT-Texteditor.png"))
        self.showNormal()
        self.statusBar().showMessage("Willkommen bei Marlems barrierefreier PQT-Texteditor")

---

def main():
    app = QtWidgets.QApplication([])
    win = MainWindow()

Code in PyCharm.

One way is to use a stylesheet.
The other is to create a derived class that provides the visual you want and use that one in place of the original QLineEdit.