Virtual Keyboard full black screen in Raspberry Pi OS using PyQt5

Question

i'm new in pyqt, and i'm trying to use Qt Virtual Keyboard on my GUI application, but there is a problem with it. When i focus on a QlineEdit, the keyboard runs on full screen mode and it does'nt appear, it's only a black screen over my application

this is how it looks (my app is still running behind)

I run exactly the same .py on Windows and it works fine. in windows

i already tried to implement the solutions to some similar questions, (like: raspbian qt virtual keyboard black top screen ) but it does'nt work for my program. I will put some code that i think, could be relevant to understand the issue.

import os
os.environ["QT_IM_MODULE"] = "qtvirtualkeyboard"

class Ventana(QMainWindow):

    def __init__(self, parent=None):
        QMainWindow.__init__(self, parent)
        uic.loadUi("desing.ui", self)

        self.lineUV.setInputMask("000")  ###example

if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    ventanaPrincipal = Ventana()
    ventanaPrincipal.showFullScreen()

sys.exit(app.exec_())

Do you know what is the problem? How can i fix it?