[PyQt] Can't neither setWindowFlags nor setFixedSize of a subwindow.

[Axel_Erfurt]

The problem is using QMainWindow as SubWindow, use QMdiSubWindow

change the first lines in usuarios.py to

from PyQt5 import QtCore, QtWidgets
from PyQt5.QtWidgets import QMdiSubWindow
  
  
class formUsers(QMdiSubWindow):

and in main.py

    def showFormUsers(self):
        self.subWindow = usuarios.formUsers()
        self.subWindow.setFixedSize(480, 300) 
        self.mdi.addSubWindow(self.subWindow)
        self.subWindow.show()