In your UIfile.py

self.setWindowFlag(QtCore.Qt.WindowType.FramelessWindowHint).

Also, in your backend file you must create

QSizeGrip(some_obj)

where some_obj is any object (frame, dutton or etc) for expanding your window, write this inside init().

Also you must write in your backend file inside your Class this:

    def move_window(e): # inside __init__()
        """Drag your window"""
        if e.buttons() == QtCore.Qt.MouseButton.LeftButton:
            try:
                self.move(self.pos() + e.globalPosition().toPoint() - self.clickPosition)
                self.clickPosition = e.globalPosition().toPoint()
                e.accept()
            except AttributeError:
                pass

def mousePressEvent(self, e):  # inside class
    self.clickPosition = e.globalPosition().toPoint()

and

self.some_obj.mouseMoveEvent = move_window # inside init()

Written for PySide6, can be adapted for PyQt